Filed Pursuant to Rule 424(b)(3)
Registration No. 333-211866

PROSPECTUS

SIGA Technologies, Inc.

Up to 35,000,000 Shares of Common Stock Issuable Upon the Exercise of Rights to Subscribe for Such Shares

SIGA Technologies, Inc. (“SIGA,” the “Company,” “we” or “us”), is distributing, at no charge, to the holders of our common stock, par value $0.0001 per share, non-transferable subscription rights to purchase shares of our common stock. The subscription rights will not be tradable. The price per share will be determined after the close of business on November 8, 2016, which is the expiration date of our offering period (the “expiration date”), and will equal the lower of $1.50 or 85% of the volume weighted average price of our shares during market hours on the expiration date, as reported on the OTC Pink Sheets. We refer to the price as so determined as the “subscription price.”

Each stockholder will receive one subscription right for each share of our common stock owned on October 12, 2016, the record date of the rights offering, and each subscription right will entitle its holder to invest $0.65 towards the purchase of shares of our common stock , which we refer to as the “basic subscription right,” at the subscription price. If you exercise your basic subscription rights in full, and other stockholders do not fully exercise their basic subscription rights, you will be entitled to an over-subscription privilege to purchase a portion of the unsubscribed common stock at the subscription price, subject to proration limitations and the potential ownership limitations set forth under “Rights Offering — Limitations on Exercise”, which we refer to as the over-subscription privilege. The number of shares that you will obtain will equal the accepted dollar amount of your investment divided by the subscription price rounded down to the nearest whole share. Each subscription right consists of a basic subscription right and an over-subscription privilege, which we refer to, together, as the subscription right.

In connection with the rights offering, we have entered into an investment agreement, or “backstop agreement,” with ST Holdings One LLC (“MacAndrews”), which is a wholly owned subsidiary of MacAndrews & Forbes LLC, Blackwell Partners LLC - Series A, Nantahala Capital Partners Limited Partnership, Nantahala Capital Partners II Limited Partnership, Silver Creek CS SAV, L.L.C. and Nantahala Capital Partners SI, LP (collectively, together with MacAndrews, the “Backstop Parties”). Under the terms of the backstop agreement, the Backstop Parties will purchase, pursuant to a separate private placement, a number of shares of common stock equal to the number of shares that are not subscribed for in the rights offering, if any, provided that to the extent MacAndrews’ acquisition of our voting stock would require a filing and approval under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 (the “HSR Act”), MacAndrews will receive non-voting convertible preferred stock in lieu of common stock, which preferred stock will automatically convert to common stock upon receipt of HSR Act approval, and will not be convertible to common stock without such HSR approval. Under the backstop agreement, the subscription price will be equal to the subscription price applicable to all shareholders under the rights offering. The Backstop Parties, taken together, will receive a fee of $1.76 million, or 5% of the maximum gross proceeds of the rights offering (the “backstop fee”), for providing the backstop commitment, payable, at the option of the Company, in cash or stock or, subject to the mutual agreement of the parties, other equity securities. In addition, the Backstop Parties will have certain registration rights with respect to shares received pursuant to the backstop agreement, as more fully described in “The Rights Offering — Backstop Agreement.” Following the rights offering and the consummation of the transactions contemplated by the backstop agreement, MacAndrews and its affiliates may be able to exert significant influence on, or may control, our affairs and actions, including matters submitted for a stockholder vote.

The total purchase price of the common stock offered in the rights offering is $35,284,792, assuming full participation, payable in cash. The net proceeds of the rights offering will be used by us for the satisfaction of PharmAthene, Inc.’s judgment against us (the “PharmAthene Judgment”), due by November 30, 2016 pursuant to our Third Amended Chapter 11 Plan as approved by the United States Bankruptcy Court for the Southern District of New York (the “Bankruptcy Court”). As of June 30, 2016, the Company’s obligation under the PharmAthene Judgment was approximately $204 million. On July 8, 2016, SIGA paid PharmAthene $20 million toward the PharmAthene Judgment, and in September and early October 2016, the Company paid an additional $100 million toward the PharmAthene Judgment. Immediately prior to the consummation of the rights offering, the remaining balance of the PharmAthene Judgment is expected to be approximately $84 million (including monthly accrued interest).

The rights will expire at 5:00 p.m., New York City time, November 8, 2016, unless extended as described herein, which date we refer to as the expiration date. We may extend the period for exercising the rights in our sole discretion; provided, however, that we may not extend the expiration date of the rights offering past November 29, 2016. Funds received in payment of the subscription price are anticipated to be held in escrow until the loan transaction described in this prospectus is consummated and the other conditions to the rights offering are satisfied or waived (if waivable), or until we definitively determine to terminate the rights offering. Such funds will not be released from escrow to or for use by us, whether for satisfaction of the PharmAthene Judgment or for any other purpose, unless we consummate the rights offering. You will have no right to rescind your subscriptions after receipt of your payment of the subscription price except as described in this prospectus. Rights that are not exercised prior to the expiration date will expire and have no value. Stockholders who do not participate in the rights offering will continue to own the same number of shares of our common stock and, if any rights are exercised, will own a smaller percentage of the total shares of our common stock issued and outstanding after the rights offering. In addition, neither the rights offering nor the loan transaction described in this prospectus will be consummated unless we determine that, upon consummation of both the rights offering and the loan transaction described in this prospectus (or through some other source of financing), we will have sufficient cash to fully satisfy the PharmAthene judgment. We may not waive these conditions. If we determine that we do not have sufficient cash to fully satisfy the PharmAthene judgment, we will terminate the rights offering and return your subscription payment to you without interest or penalty. In addition, if we are unable to satisfy the PharmAthene judgment, PharmAthene may be entitled to all the equity of the Company. If PharmAthene receives all the equity of the Company, you will lose any shares of the Company’s common stock that you currently hold and will therefore suffer a complete loss of your equity investment in the Company (other than any subscription payments made in connection with the rights offering, which will be returned to you as described herein).

We are distributing the rights and offering the common stock directly to you. We have not employed any brokers, dealers or underwriters in connection with the solicitation or exercise of rights in the rights offering and no commissions, fees or discounts will be paid in connection with the rights offering. American Stock Transfer & Trust Company, LLC is acting as the subscription agent. While certain of our directors, officers and other employees may solicit responses from you, those directors, officers and other employees will not receive any commissions or compensation for their services other than their normal compensation.

Exercising your subscription rights for the common stock involves risks. See “Risk Factors” beginning on page 13 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities regulators have approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Our securities are not being offered in any jurisdiction where the offer is not permitted under applicable local laws.

If you have any questions or need further information about this rights offering, please call D.F. King & Co., Inc., the information agent for the rights offering, toll free at 1-800-207-2872, or by email at infoagent@dfking.com.

The date of this prospectus is October 21, 2016.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

You should rely only on the information contained in this prospectus or any free writing prospectus we may authorize to be delivered to you. We have not authorized anyone to provide you with different or additional information. We are not making an offer of securities in any state or other jurisdiction where the offer is not permitted. You should not consider any information in this prospectus to be investment, legal or tax advice. We encourage you to consult your own counsel, accountant and other advisors for legal, tax, business, financial and related advice regarding an investment in our securities.

Unless we otherwise indicate or unless the context requires otherwise, all references in this prospectus to the “Company,” “SIGA,” “we,” “us” or “our” refer to SIGA Technologies, Inc. and its subsidiaries.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus contains certain forward-looking statements regarding, among other things, our anticipated financial and operating results. Investors are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. We undertake no obligation to publicly release any modifications or revisions to these forward-looking statements to reflect events or circumstances occurring after the date hereof or to reflect the occurrence of unanticipated events, except to the extent required by federal securities laws. Such forward-looking statements involve known and unknown risks, uncertainties, and other factors that may cause our actual results, performance, or achievements to be materially different from any future results, performance, or achievements expressed or implied by such forward-looking statements.

The words “anticipate,” “believe,” “estimate,” “expect,” “intend,” “will,” “should,” “may,” “plan,” and similar expressions, as they relate to us or our management, are intended to identify forward-looking statements. Such statements reflect our current views with respect to future events and are subject to certain risks, uncertainties, and assumptions. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those described herein as anticipated, believed, estimated, expected, intended, or planned. We assume no obligations and do not intend to update these forward-looking statements.

Readers are also urged to carefully review and consider the various disclosures made by us which attempt to advise interested parties of the factors that affect our business, including without limitation the disclosures made under the caption “Management’s Discussion and Analysis” and under the caption “Risk Factors” included herein.

PROSPECTUS SUMMARY

The following summary provides an overview of certain information about us and the rights offering and may not contain all the information that is important to you. This summary is qualified in its entirety by, and should be read together with, the information contained in other parts of this prospectus. You should read this entire prospectus carefully before making a decision about whether to invest in our securities.

SIGA Technologies, Inc.

We are a company specializing in the development and commercialization of solutions for serious unmet medical needs and biothreats. Our lead product is TPOXX^®, also known as Tecovirimat or ST-246®, an orally administered antiviral drug that targets orthopoxvirus infections. While TPOXX^® is not yet approved as safe or effective by the U.S. Food & Drug Administration (“FDA”), it is a novel small-molecule drug that is being developed with support from Biomedical Advanced Research and Development Authority (“BARDA”) and delivered to the U.S. Strategic National Stockpile (the “Strategic Stockpile”) under Project BioShield.

We were incorporated in the State of Delaware in 1995. Our principal executive offices are located at 660 Madison Avenue, Suite 1700, New York, NY 10065. Our telephone number is (212) 672-9100. Our website is www.siga.com. Information contained on our website does not constitute a part of this prospectus.

Recent Developments

On October 13, 2016, Eric A. Rose entered into an amended and restated employment agreement pursuant to which he resigned from the position of Chief Executive Officer of the Company and was appointed Executive Chairman of the Board of Directors of the Company. On the same day, Phillip Louis Gomez, III entered into an employment agreement pursuant to which he became the Company’s Chief Executive Officer.

Chapter 11 Case

On September 16, 2014, the Company filed a voluntary petition for relief under chapter 11 of Title 11 of the United States Code (the “Bankruptcy Code”) in the United States Bankruptcy Court for the Southern District of New York (the “Bankruptcy Court”) chapter 11 Case Number 14-12623 (SHL). The Company operated its business as a “debtor-in-possession” until its emergence from chapter 11 of the Bankruptcy Code on April 12, 2016. The Company did not apply the provision of fresh start accounting as ownership of existing shares of the Company’s common stock remained unaltered by the Third Amended Chapter 11 Plan.

The Company commenced the chapter 11 case to preserve its ability to satisfy its commitments under its contract with BARDA (the “BARDA Contract”) and to maintain its operations, which likely would have been jeopardized by the enforcement of a judgment stemming from the litigation with PharmAthene (see “PharmAthene Litigation” below). While operating as a debtor-in-possession under chapter 11, the Company pursued an appeal of the Delaware Court of Chancery’s final order and judgment (the “Delaware Court of Chancery Final Order and Judgment”), without having to post a bond.

Plan of Reorganization

On April 7, 2016, the Company filed its Third Amended Chapter 11 Plan (the “Plan”), which was supported by the official committee of unsecured creditors appointed in the Company’s chapter 11 case (the “UCC”). The Plan, as more fully described below, addresses, among other things, how the Company will treat and satisfy its liabilities relating to the period prior to the commencement of its chapter 11 case, including all claims held by PharmAthene. On April 8, 2016, the Bankruptcy Court confirmed the Plan and on April 12, 2016, the Plan became effective (the “Effective Date of the Plan”).

The Plan provides that, among other things:

In addition, the Plan requires the Company to comply with certain affirmative and negative covenants from the Effective Date of the Plan until the covenants are terminated as provided under the Plan, and if the Company breaches any covenant, PharmAthene is entitled to exercise certain remedies provided in the Plan — See “Business — Plan of Reorganization”.

PharmAthene Litigation

After several years of litigation and remands, the Delaware Supreme Court on December 23, 2015 affirmed the Delaware Court of Chancery Final Order and Judgment in which the Delaware Court of Chancery (the “Court of Chancery”) awarded PharmAthene approximately $195 million, including pre-judgment interest up to January 15, 2015. As of June 30, 2016 the accrued obligation under the PharmAthene Judgment, including post-judgment interest, was approximately $204 million. On July 8, 2016, SIGA paid PharmAthene $20 million toward the PharmAthene Judgment, and in September and early October 2016, the Company paid an additional $100 million toward the PharmAthene Judgment. Immediately prior to the consummation of the rights offering, the remaining balance of the PharmAthene Judgment is expected to be approximately $84 million (including monthly accrued interest). The PharmAthene Judgment will be satisfied in accordance with the Plan, as described in “Business — Plan of Reorganization.”

Going Concern

The Company’s ability to continue as a going concern is impacted by the PharmAthene Judgment, as well as by the uncertainty attendant to the exact manner in which PharmAthene’s claim will be treated under the Plan. As of June 30, 2016, the accrued obligation under the Delaware Court of Chancery Final Order and Judgment, including post-judgment and Plan-specified interest, was approximately $204 million. In addition, as of June 30, 2016, the Company has a net capital deficiency of $304 million. These factors raise substantial doubt about the Company’s ability to continue as a going concern. As such, the realization of assets and the satisfaction of liabilities are subject to uncertainties. The financial statements included in this prospectus do not include any adjustments related to the recoverability and classification of assets or the amounts and classification of liabilities or any other adjustments that might be necessary should the Company be unable to continue as a going concern.

The Rights Offering

date, either as a holder of record or, in the case of shares held of record by brokers, banks, or other nominees, on your behalf, as a beneficial owner of such shares. We determined the investment amount of $0.65 per basic subscription right by dividing the amount of gross proceeds we wish to raise for the purposes described herein in “Use of Proceeds” ($35,284,792) by the number of rights we are distributing in the rights offering (54,284,296).

Your basic subscription rights will entitle you to invest $0.65 towards the purchase of shares of our common stock for each share of stock that you own on the record date, upon timely delivery of the required documents and payment of the subscription price. For example, if you owned 20 shares of Common Stock on the record date, you would receive 20 rights and would have the right to invest $0.65 for each share of Common Stock you own as of the record date at the subscription price. If you have invested $13.00, and if on the expiration date of the rights offering the volume weighted average price of our common stock as reported on the OTC Pink Sheets is $2.50 per share, the subscription price will be $1.50 and you would receive a rounded down 8 shares and a refund of $1.00. If you have invested $13.00 and if on the expiration date of the rights offering the volume weighted average price of our common stock during market hours as reported on the OTC Pink Sheets is $1.60 per share, the subscription price will be $1.36 per share (which constitutes 85% of $1.60), you would receive a rounded down 9 shares and a refund of $0.76.

the properly exercised over-subscription privilege requests based on the amounts invested by stockholders participating in the rights offering, then the available shares will be prorated among those who properly exercised over-subscription privileges based on the number of shares each rights holder subscribed for under the basic subscription right after that number is determined when measured against the subscription price. If this pro rata allocation results in any stockholder receiving a greater number of shares of common stock than the stockholder subscribed for pursuant to the exercise of the over-subscription privilege, then such stockholder will be allocated only that number of shares for which the stockholder oversubscribed, and the remaining shares of common stock will be allocated among all other stockholders exercising the over-subscription privilege on the same pro rata basis described above. The proration process will be repeated until all shares of common stock have been allocated or all over-subscription exercises have been fulfilled, whichever occurs first.

presumed volume weighted average price during market hours of $1.60 per share on the expiration date) we will issue approximately 25,944,700 shares and have 80,228,996 shares of common stock issued and outstanding (in each case, not including any shares that may be issued in payment of the fee under the backstop agreement).

the subscription agent will return in cash the excess amount to you by mail, without interest or penalty, as soon as practicable after the expiration date of the rights offering.

require us to return subscription funds consistent with Rule 10b-9 promulgated under the Securities Exchange Act of 1934, as amended (the “Exchange Act”).

The rights offering is subject to the following conditions:

We may not waive any of the conditions set forth in the first three bullets above.

If we cancel or terminate the rights offering, in whole or in part, all affected subscription rights will expire without value and all funds received in connection with the rights offering will be returned as soon as practicable, without interest or penalty, to those persons who exercised their subscription rights.

the rights offering, for providing the backstop commitment, payable, at the option of the Company, in cash or stock or, subject to the mutual agreement of the parties, other equity securities. In addition, the Backstop Parties will have certain registration rights with respect to shares received pursuant to the backstop agreement, as more fully described in “The Rights Offering — Backstop Agreement.”

For additional information concerning the rights offering, see “The Rights Offering,” beginning on page 38.

Before investing in our common stock, you should carefully read and consider the information set forth in “Risk Factors” beginning on page 13 and all other information appearing elsewhere in this prospectus.

SELECTED FINANCIAL DATA

The selected financial data for the years ended December 31, 2015, 2014 and 2013 and the consolidated balance sheet data as of December 31, 2015 and 2014 have been derived from our audited consolidated financial statements included elsewhere in this prospectus. The selected financial data for the six months ended June 30, 2016 and 2015 and the consolidated balance sheet data as of June 30, 2016 and 2015 have been derived from our unaudited condensed consolidated financial statements included elsewhere in this prospectus. The selected financial data for the years ended December 31, 2012 and 2011 and the consolidated balance sheet data as of December 31, 2013, 2012 and 2011 have been derived from applicable audited consolidated financial statements not included in this prospectus. The following table should be read in conjunction with “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” and the consolidated financial statements and related notes to those statements included elsewhere in this prospectus.
   

SUPPLEMENTARY FINANCIAL INFORMATION

Below is selected quarterly financial data for the three months ended March 31, 2016, which has been derived from our unaudited condensed consolidated financial statements included in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2016, and the three months ended June 30, 2016, which has been derived from our unaudited condensed consolidated financial statements included elsewhere in this prospectus. For selected quarterly financial data for each quarter of the years ended December 31, 2015 and 2014, see Note 14 to our audited consolidated financial statements included elsewhere in this prospectus. The following table should be read in conjunction with “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” and the consolidated financial statements and related notes to those statements included elsewhere in this prospectus.

RISK FACTORS

This prospectus contains forward-looking statements and other prospective information relating to future events. These forward-looking statements and other information are subject to risks and uncertainties that could cause our actual results to differ materially from our historical results or currently anticipated results including the following:

Risks Related to the Rights Offering

The subscription rights are non-transferable and there is no market for the subscription rights.

Other than in very limited circumstances, you may not sell, give away or otherwise transfer your subscription rights. Because the subscription rights are non-transferable, there is no market or other means for you to directly realize any value associated with the subscription rights. You must exercise the subscription rights in order to realize any potential value.   

The conditions to the rights offering may not be fulfilled, and even if they are fulfilled we may cancel the rights offering at any time, for any reason or no reason. If we cancel the rights offering, neither we nor the subscription agent will have any obligation to you except to return your subscription payments.

We may unilaterally cancel the rights offering at any time in our sole discretion, for any reason or no reason. We expect to cancel the rights offering if one of the conditions outlined under “The Rights Offering – Termination Rights; Conditions to the Rights Offering” is not satisfied. There can be no assurance that the conditions to the rights offering, including the consummation of the Loan Transaction, will be satisfied. If we cancel the rights offering, the subscription rights will be void and will have no value, and neither we nor the subscription agent will have any obligation with respect to the subscription rights except to return, without interest or penalty, any subscription payments actually received.

To exercise your subscription rights, you must act promptly and follow the subscription instructions carefully.

If you desire to participate in the rights offering, you must act promptly to ensure that all required forms and payments are actually received by the subscription agent at or prior to 5:00 p.m., New York City time, on November 8, 2016, the current expiration date of the rights offering. If you fail to complete and sign the required subscription forms, send an incorrect payment amount, or otherwise fail to follow the subscription procedures that apply to your desired transaction, the subscription agent may, depending on the circumstances, reject your subscription or accept it to the extent of the payment received. Neither we nor the subscription agent has any obligation to contact you concerning, or attempt to correct, an incomplete or incorrect subscription form or payment. We have the sole discretion to determine whether a subscription exercise properly follows the subscription procedures. See “The Rights Offering” for additional details regarding exercise of your subscription rights.

Because our management will have broad discretion over the use of the net proceeds from the rights offering, you may not agree with how we use the proceeds, and we may not invest the proceeds successfully.

While we currently anticipate that we will use the net proceeds of the rights offering, in combination with other sources of liquidity, to pay the PharmAthene Judgment, our management may allocate the proceeds among these purposes as it determines is appropriate. In addition, market factors may require our management to allocate portions of the proceeds for other purposes. Accordingly, you will be relying on the judgment of our management with regard to the use of the proceeds from the rights offering, and you will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. It is possible that the proceeds will be invested in a way that does not yield a favorable, or any, return for the Company.

If you do not exercise all of your subscription rights in the rights offering, you may suffer dilution of your percentage ownership of our common stock.

To the extent that you do not exercise your subscription rights to subscribe for shares of our common stock, your proportionate ownership in us will be reduced by the exercise by other holders of our common stock of their subscription rights and/or the associated backstop. Further, we will not be able to determine the number of shares of common stock outstanding after the rights offering, and thus the magnitude of any dilution, until after expiration of the rights offering. The number of shares of common stock outstanding after the rights offering will depend on the subscription price once it is established. For example, based on 54,284,296 shares of common stock outstanding as of October 12, 2016, assuming no other transactions by us involving our common stock prior to the expiration of the

rights offering, and if the rights offering is fully subscribed and the subscription price is determined to be $1.50 per share (which is the maximum possible price per share in the rights offering), we will issue approximately 23,523,195 shares and have approximately 77,807,491 shares of common stock issued and outstanding (in each case, not including any shares that may be issued in payment of the fee under the backstop agreement). However, by way of further illustration, based on the same number of shares outstanding, assuming no other transactions by us involving our common stock before the expiration date and assuming the rights offering is fully subscribed at $1.36 per share (which would equate to 85% of a presumed volume weighted average price during market hours of $1.60 per share on the expiration date) we will issue approximately 25,944,700 shares and have 80,228,996 shares of common stock issued and outstanding (in each case, not including any shares that may be issued in payment of the fee under the backstop agreement).

Following the rights offering and the consummation of the transactions contemplated by the backstop agreement, MacAndrews and its affiliates may be able to exert significant influence on, or may control, our affairs and actions, including matters submitted for a stockholder vote.

Currently, MacAndrews beneficially owns 13,509,722 shares of common stock, which is equivalent to 24.89% of our currently issued and outstanding common stock as of October 12, 2016. The number of shares of common stock held by MacAndrews after the rights offering will depend on the subscription price once it is established. For example (assuming the Company elects to pay the fee under the backstop agreement in cash), if no stockholders subscribe for shares in this rights offering (other than MacAndrews) and MacAndrews is required to purchase the maximum number of shares issuable pursuant to the backstop agreement (in the form of common stock), then MacAndrews will own 47.60% of our outstanding common stock following the closing of the rights offering and the consummation of the transactions contemplated by the backstop agreement if the rights offering is priced at $1.50 per share, or 49.18% of our outstanding common stock following the closing of the rights offering and the consummation of the transactions contemplated by the backstop agreement if the rights offering is priced at $1.36 per share. As a result, in such scenarios MacAndrews and its affiliates would have considerable influence over, or possibly control, our corporate affairs and actions, including matters submitted for a stockholder vote. The interests of MacAndrews and its affiliates may be different than your interests.

You may not receive all of the shares of common stock for which you subscribe.

Holders who fully exercise their basic subscription rights will be entitled to subscribe for additional amounts in the exercise of their over-subscription privileges. Under the terms of the rights offering, over-subscription privileges will be allocated pro rata among rights holders who over-subscribed, based on the over-subscription amounts at the subscription price for which they have subscribed. We cannot guarantee that you will receive all or any portion of the shares for which you over-subscribed. If the prorated amount of shares allocated to you at the subscription price in connection with your over-subscription privilege is less than your over-subscription request, then the excess funds held by the subscription agent on your behalf will be returned to you, without interest or penalty, as soon as practicable after the rights offering has expired and all prorating calculations and reductions contemplated by the terms of the rights offering have been effected, and we will have no further obligations to you.

In the event that the exercise by a stockholder of the basic subscription right or the over-subscription privilege could, as determined by the Company in its sole discretion, potentially result in a limitation on the Company’s ability to use NOLs we may, but are under no obligation to, reduce the exercise by such stockholder of the basic subscription right and/or the over-subscription privilege to such number of shares of common stocks as the Company in its sole discretion shall determine to be advisable in order to preserve the Company’s ability to use NOLs. If the amount of shares allocated to you is less than your subscription request, then the excess funds held by the subscription agent on your behalf will be returned to you, without interest or penalty, as soon as practicable after the rights offering has expired and all prorating calculations and reductions contemplated by the terms of the rights offering have been effected, and we will have no further obligations to you.

The market price of our common stock may decline before or after the subscription rights expire.

We cannot assure you that the market price of our common stock will not decline after you elect to exercise your subscription rights and obtain shares as computed with respect to the subscription price when it is determined. Accordingly, we cannot assure you that following the exercise of your subscription rights you will be able to sell your common stock at a price equal to or greater than the subscription price. Until shares are delivered upon expiration of the rights offering, you will not be able to sell the shares of our common stock that you purchase in the rights

offering. Certificates (physical, electronic or book entry from) representing shares of our common stock purchased will be delivered as soon as practicable after expiration of the rights offering. We will not pay you interest on funds delivered to the subscription agent pursuant to the exercise of subscription rights.

The rights offering may cause the price of our common stock to decline.

Depending upon the trading price of our common stock at the time of our announcement of the rights offering and its terms, including the subscription price as determined upon the expiration of the rights offering, together with the number of shares of common stock we propose to issue and ultimately will issue if the rights offering is completed, the rights offering may result in an immediate decline in the market value of our common stock. This decline may continue after the completion of rights offering. If that occurs, you may have committed to buy shares of common stock in the rights offering at a price greater than the prevailing market price following the expiration date. Further, if a substantial number of rights are exercised and the holders of the shares received upon exercise of those rights choose to sell some or all of those shares, the resulting sales could depress the market price of our common stock. There is no assurance that, following the expiration date, you will be able to sell your common stock at a price equal to or greater than the subscription price.

The subscription price determined for the rights offering is not an indication of the fair value of our common stock.

In determining the method for obtaining the subscription price at the expiration of the rights offering period, our Board of Directors considered a number of factors, including, but not limited to, the price at which our shareholders might be willing to participate in the rights offering, historical and current trading prices for our common stock including volatility, the amount of proceeds desired, the potential need for liquidity and capital, potential market conditions, and the desire to provide an opportunity to our shareholders to participate in the rights offering. In conjunction with its review of these factors, our Board of Directors also reviewed a range of discounts to market value represented by the subscription prices in various prior rights offerings by other public companies. The subscription price does not necessarily bear any relationship to the book value of our assets, results of operations, cash flows, losses, financial condition or any other established criteria for value. You should not consider the subscription price as an indication of the fair value of our common stock. After the date of this prospectus, our common stock may trade at prices above or below the subscription price.

Risks Related to Our Common Stock

If we are unable to consummate the rights offering in a manner that provides us with enough proceeds, along with our other sources of funds, to pay PharmAthene the full amount of its claims against us, you may lose your entire investment.

As of June 30, 2016, we owed PharmAthene, Inc. (“PharmAthene”) approximately $204 million and post-judgment interest continues to accrue on the damages amount. If we are unable to satisfy this claim, PharmAthene may be entitled to all the equity of the Company. If PharmAthene receives all the equity of the Company, you will no longer have any equity interest in the Company and will suffer a complete loss of your equity investment in the Company.

The substantial loss from the PharmAthene litigation, combined with the Company’s net capital deficiency of $295 million, has led our independent registered public accounting firm to express substantial doubt about our ability to continue as a going concern.

The substantial loss from the PharmAthene litigation (as described in “Legal Proceedings”), combined with the Company’s net capital deficiency of $295 million as of December 31, 2015, led our independent registered public accounting firm to express substantial doubt about our ability to continue as a going concern in its report as to our financial statements as of and for the year ended December 31, 2015. If we are forced to liquidate or are otherwise unable to continue as a going concern, investors will likely lose all of their investment in our Company.

Our stock price is, and we expect it to remain, volatile, which could limit investors’ ability to sell stock at a profit.

The volatile price of our stock makes it difficult for investors to predict the value of their investments, to sell shares at a profit at any given time, or to plan purchases and sales in advance. A variety of factors may affect the market price of our common stock. These include, but are not limited to:

Additionally, because the volume of trading in our stock fluctuates significantly at times, any information about us in the media may result in significant volatility in our stock price.

We will not be able to control many of these factors, and we believe that period-to-period comparisons of our financial results will not necessarily be indicative of our future performance.

In addition, the stock market in general, and the market for biotechnology companies in particular, has experienced extreme price and volume fluctuations that may have been unrelated or disproportionate to the operating performance of individual companies. These broad market and industry factors may seriously harm the market price of our common stock, regardless of our operating performance.

If securities or industry analysts publish inaccurate or unfavorable research about our business, our stock price could decline.

The trading market for our common stock will depend in part on the research and reports that securities or industry analysts publish about us or our business. If one or more of the analysts who cover us downgrade our common stock or publish inaccurate or unfavorable research about our business, our common stock price would likely decline.

A future issuance of preferred stock may adversely affect the rights of the holders of our common stock.

Our certificate of incorporation allows our Board of Directors to issue up to 20,000,000 shares of preferred stock and to fix the voting powers, designations, preferences, rights and qualifications, limitations or restrictions of these shares without any further vote or action by the stockholders. The rights of the holders of common stock will be subject to, and could be adversely affected by, the rights of the holders of any preferred stock that we may issue in the future. The issuance of preferred stock, while providing desirable flexibility in connection with our future activities, could also have the effect of making it more difficult for a third party to acquire a majority of our outstanding voting stock, thereby delaying, deferring or preventing a change of control.

Concentration of ownership of our capital stock could delay or prevent a change of control.

Our directors, executive officers and principal stockholders, including MacAndrews, beneficially own a significant percentage of our common stock, which percentages may increase as a result of the rights offering as well as issuance of shares under the backstop agreement. They also have, through the exercise or conversion of certain securities, the right to acquire additional common stock. As a result, these stockholders, if acting together, have the ability to influence the outcome of corporate actions requiring stockholder approval. Additionally, this concentration of ownership may have the effect of delaying or preventing a change of control of SIGA. As of the most recent available information, directors, executive officers and principal stockholders beneficially owned approximately 30% of our outstanding stock.

Risks Related to Our Chapter 11 Case

Under the Plan, equity investors could incur a total loss of their investment if the Company does not pay the PharmAthene Judgment within an allotted time period.

Under the Plan, the Company has until November 30, 2016 to fully satisfy the PharmAthene Judgment. If the PharmAthene Judgment is not satisfied within the allotted time period, and provided that an alternative mechanism is not agreed-upon by the Company and PharmAthene, then the Company would be required to deliver to PharmAthene 100% of newly-issued stock of SIGA and all existing shares of the Company’s common stock would be cancelled with no distribution to existing stockholders on account thereof.

Under the Plan, we have emerged from bankruptcy but we are subject to various restrictive covenants which may impede our operations until the PharmAthene Judgment is satisfied.

The Plan requires that we comply with certain restrictive covenants regarding our operations until the PharmAthene Judgment is satisfied under the Plan. Compliance with these requirements may have a material adverse effect on our ability to operate our business.

If we default on the restrictive covenants contained in the Plan, the composition of the Board of Directors will be significantly altered and the Company’s use of cash resources will be highly restricted.

Under certain circumstances, as provided for in the Plan, a breach of the covenants contained therein could lead to an event of default. If an event of a default were to occur, the composition of our Board of Directors would be altered, with PharmAthene designees constituting a majority of our Board of Directors. Additionally, the Company’s usage of cash on hand would be subject to supervision by PharmAthene and could be restricted. These changes could have a significant adverse effect on the operations and financial condition of the Company and our ability to satisfy the PharmAthene Judgment, which failure could lead to a total loss of your investment in the Company.

Risks Related to Our Financial Position and Need for Additional Financing

Our common stock was delisted by NASDAQ, which could limit the liquidity of our common stock, increase its volatility and hinder our ability to raise capital.

On March 20, 2015, the Company’s common stock was suspended from trading on the NASDAQ Global Market at the opening of business and began trading on the OTC Pink Sheets, an inter-dealer electronic quotation and trading system for equity securities. This delisting has limited the liquidity of our common stock, and could increase its volatility and hinder our ability to raise capital. Some investors may perceive our common stock to be less attractive because it is traded on the OTC Pink Sheets. In addition, as a company quoted on the OTC Pink Sheets, we do not attract the extensive analyst coverage that accompanies companies listed on national exchanges. Further, institutional and other investors may have investment guidelines that restrict or prohibit investing in securities traded on the OTC Pink Sheets. These factors may have an adverse impact on the trading and price of our common stock.

We have incurred operating losses since our inception and expect to incur net losses for the foreseeable future.

We incurred net operating losses of approximately $31.0 million and $209.7 million for the years ended December 31, 2015 and 2014, respectively. As of December 31, 2015, 2014 and 2013, our accumulated deficit was approximately $461.4 million, $442.0 million and $156.5 million, respectively. We expect to continue to have significant operating expenses and will need to generate significant revenues to achieve and maintain profitability.

Our ability to fund operations is substantially dependent on cash flows from the BARDA Contract. If we do not achieve positive cash flows, we cannot guarantee that we can sustain or enhance our current level of operations. We expect that cash flows will fluctuate significantly and could be delayed from one quarter to another based on several factors. If cash flows grow slower than we anticipate, or if operating expenses or other expenses exceed our expectations or cannot be adjusted accordingly, then our business, results of operations, financial condition and cash flows will be materially and adversely affected.

Future acquisitions, strategic investments, partnerships or alliances could be difficult to identify and integrate, divert the attention of management, disrupt our business, dilute stockholder value and adversely affect our operating results and financial condition.

We may in the future seek to acquire or invest in businesses, products or technologies that we believe could complement or expand our services, enhance our technical capabilities or otherwise offer growth opportunities. The pursuit of potential acquisitions may divert the attention of management and cause us to incur various expenses in identifying, investigating and pursuing businesses, we may not be able to find and identify desirable acquisition targets or be successful in entering into an agreement with any particular target or consummating any such agreement. We may not be able to integrate successfully the acquired personnel, operations and technologies, or effectively manage the combined business following the acquisitions. All of these potential difficulties might be compounded by uncertainty surrounding our ability to pay the PharmAthene Judgment. Acquisitions could also result in dilutive issuances of equity securities or the issuance of debt, which could adversely affect our operating results. In addition, if an acquired business fails to meet our expectations, our operating results, business and financial condition may suffer.

Apart from the funds necessary to satisfy the PharmAthene Judgment, we may need additional funding, which may not be available to us, and which may force us to delay, reduce or eliminate any of our product development programs or commercialization efforts.

While we have raised funds through credit facilities and the issuance of new equity or the exercise of options or warrants in the past, there is no guarantee that we will continue to be successful in raising such funds. If we are unable to raise additional funds, apart from the funds necessary to satisfy the PharmAthene Judgment, we could be forced to discontinue, cease or limit certain operations and equity investors could experience significant or total losses of their investments. Our cash flows may fall short of our projections or be delayed, or our expenses may increase, which could result in our capital being consumed significantly faster than anticipated. Our annual operating needs vary from year to year depending upon the amount of cash generated through the BARDA Contract, contracts, grants, licenses, the amount of projects we undertake, and the amount of resources we expend in connection with acquisitions, all of which may materially differ from year to year and may adversely affect our business.

Even assuming consummation of the rights offering and the Loan Transaction on the terms described herein, we may require additional financing and we may not be able to raise additional funds. If we are able to obtain additional financing through the sale of equity or convertible debt securities, such sales may contain terms, such as liquidation and other preferences that are not favorable to us or our stockholders. If we raise additional funds through collaboration and licensing arrangements with third parties, it may be necessary to relinquish valuable rights to our technologies or product candidates or grant licenses on terms that may not be favorable to us. Debt financing arrangements, if available, may require us to pledge certain assets or enter into covenants that would restrict our business activities or our ability to incur further indebtedness and may be at interest rates and contain other terms that are not favorable to our stockholders.

Indebtedness may make it more difficult to obtain additional financing or reduce our flexibility to act in our best interests.

Upon consummation of the Loan Transaction, we will be obligated to make monthly interest payments on the outstanding principal amount in addition to monthly principal payments. From and after consummation of the Loan Transaction, the level of our indebtedness could affect us by: making it more difficult to obtain additional financing for working capital, capital expenditures, debt service requirements or other purposes; shortening the duration of available revolving credit because lenders may seek to avoid conflicting maturity dates; constraining our ability to react quickly in an unfavorable economic climate or to changes in our business or the pharmaceutical industry; or potentially requiring the dedication of substantial amounts to service the repayment of outstanding debt, including periodic interest payments, thereby reducing the amount of cash available for other purposes. In addition, the Loan

Agreement (as defined in “The Rights Offering—Simultaneous Loan Transaction”) contains customary covenants which could impact our ability to obtain additional financing and restrict our flexibility in carrying out our business strategy.

Our indebtedness under the Loan Agreement will be secured by a first priority lien on all of our existing and after-acquired property. If we default on our obligations under the Loan Agreement, our lender could foreclose on our assets.

We may issue additional debt or incur other types of indebtedness in the future, subject to compliance with the terms of the Loan Agreement.

Risks Related to Our Dependence on U.S. Government Contracts and Grants

We currently expect to derive substantially all of our foreseeable future revenue from sales of TPOXX^® under our contract with the U.S. Biomedical Advanced Research and Development Authority (“BARDA”) in addition to contracts and grants from various agencies of the U.S. government. If BARDA demand for TPOXX^® is reduced, our business, financial condition and operating results could be materially harmed.

The BARDA Contract does not necessarily increase the likelihood that we will secure future comparable contracts with the U.S. government. The success of our business and our operating results for the foreseeable future are substantially dependent on the terms of TPOXX^® sales to the U.S. government, including price per course, the number and size of doses in a course and the timing of deliveries.

Furthermore, substantially all of our revenues for the years ended December 31, 2015, 2014 and 2013, respectively, were derived from contracts and grants other than the BARDA Contract. Our current revenue is primarily derived from one BARDA development contract scheduled to substantially conclude in February 2018. There can be no assurance that we will recognize the revenue from the BARDA Contract in the time periods we anticipate or at all, or that we will be able to secure future contracts or grants. Failure to recognize such revenue or secure such contracts or grants could have a material adverse effect on our results of operations.

The pricing under our fixed-price government contracts and grants is based on estimates of the time, resources and expenses required to perform these contracts and grants. If our estimates are not accurate, we may not be able to earn an adequate return or may incur a loss under these arrangements.

Our existing contract with BARDA for TPOXX^® includes fixed-price components. We expect that our future contracts and grants with the U.S. government for TPOXX^® as well as contracts and grants for biodefense product candidates that we successfully develop also may be fixed-price arrangements. Under a fixed-price contract or grant, we are required to deliver our products at a fixed price regardless of the actual costs we incur and to absorb any cost in excess of the fixed price. Estimating costs that are related to performance in accordance with contract or grant specifications is difficult, particularly where the period of performance is over several years. Our failure to anticipate technical problems, estimate costs accurately or control costs during performance of a fixed-price contract or grant could reduce the profitability of a fixed-price contract or grant or cause a loss, which could in turn harm our operating results.

Product deliveries of TPOXX^® since December 31, 2014 have been at a provisional dosage of 600 mg administered twice per day (1,200 mg per day). This is a change from the provisional dosage that was in effect when product deliveries were made in 2013 and 2014 (600 mg per day). In 2013 and 2014, the provisional dosage of courses delivered to the Strategic Stockpile was 600 mg administered once per day. The change in the provisional dosage is based on FDA guidance received by the Company in 2014, subsequent to the deliveries of 1.3 million courses of TPOXX^®. Based on the provisional dosage of 600 mg administered twice per day, SIGA currently expects to supplement previously delivered courses of TPOXX^®, at no additional cost to BARDA, with additional capsules so that all of the courses previously delivered to BARDA will be at the new provisional dosage. The Company expects to incur significant incremental costs when previously delivered courses are supplemented. The provisional dosage for TPOXX^® may be subject to additional changes in the future based on FDA guidance.

Our U.S. government contracts and grants require ongoing funding decisions by the government. Reduced or discontinued funding of these contracts and grants could cause our financial condition and operating results to suffer materially.

Our principal customer for TPOXX^® at the present time is the U.S. government. We anticipate that the U.S. government will also be the principal customer for any other biodefense product that we successfully develop. A U.S. government program, such as Project BioShield, may be implemented through the award of many different individual grants, contracts and subcontracts. The funding of government programs is subject to Congressional appropriations, generally made on a fiscal year basis even though a program may continue for several years. Our government customers are subject to political considerations and stringent budgetary constraints. Our government customers are also subject to uncertainties as to continued funding of their budgets. Additionally, government-funded development grants and contracts typically consist of a base period of performance followed by successive option periods for performance of certain future activities. The value of the goods and services provided during such option periods, which are exercisable in the sole discretion of the government, may constitute the majority of the total value of the underlying contract. If levels of government expenditures and authorizations for biodefense decrease or shift to programs in areas where we do not offer products or are not developing product candidates, our business, revenues and operating results may suffer materially.

Our future business may be harmed as a result of the government contracting process, which can be a competitive bidding process that may involve risks not present in the commercial contracting process.

We expect that a significant portion of the business that we will seek in the near future will be under government grants, contracts or subcontracts, which may be awarded through competitive bidding. Competitive bidding for government contracts and grants presents a number of risks that are not typically present in the commercial contracting process, which may include:

The U.S. government may choose to award future contracts and grants for the supply of smallpox antivirus and other biodefense product candidates that we are developing to our competitors instead of to us. If we are unable to win particular contracts and grants, we may not be able to operate in the market for products that are provided under those contracts and grants for a number of years. If we are unable to obtain new contracts and grants over an extended period, or if we fail to anticipate all of the costs and resources that will be required to secure and fulfill such contracts and grants, our growth strategy and our business, financial condition, and operating results could be materially adversely affected.

The success of our business with the U.S. government depends on our compliance with laws, regulations and obligations under our U.S. government contracts and grants and various federal statutes and authorities.

Our business with the U.S. government is subject to specific procurement regulations and a variety of other legal and compliance obligations. These laws and rules include those related to:

In addition, before awarding us any contract or grant, the U.S. government could require that we respond satisfactorily to a request to substantiate our commercial viability and industrial capabilities. Compliance with these obligations increases our performance and compliance costs. Failure to comply with these regulations and requirements could lead to suspension or debarment, for cause, from government contracting or subcontracting for a period of time. The termination of a government contract or grant or relationship as a result of our failure to satisfy any of these obligations would have a material negative impact on our operations and harm our reputation and ability to procure other government contracts or grants in the future.

Unfavorable provisions in government contracts and grants, some of which may be customary, may harm our future business, financial condition and potential operating results.

Government contracts and grants customarily contain provisions that give the government substantial rights and remedies, many of which are not typically found in commercial contracts, including (but not limited to) provisions that allow the government to:

Generally, government contracts and grants contain provisions permitting unilateral termination or modification, in whole or in part, at the government’s convenience. Under general principles of government contracting law, if the government terminates a contract or grant for convenience, the terminated company may recover only its incurred or committed costs, settlement expenses and profit on work completed prior to the termination. If the government terminates a contract or grant for default, the defaulting company is entitled to recover costs incurred and associated profits on accepted items only and may be liable for excess costs incurred by the government in procuring undelivered items from another source. Our government contracts and grants, including the BARDA Contract, could be terminated under these circumstances.

Some government contracts and grants permit the government the right to use, for or on behalf of the U.S. government, any technologies developed by the contractor under a government contract or grant. If we were to develop technology under a contract or grant with such a provision, we might not be able to prohibit third parties, including our competitors, from using that technology in providing products and services to the government.

Changing political or social factors and opposition, including protests and potential related litigation, may delay or impair our ability to market TPOXX^® and our biodefense product candidates and may require us to spend time and money to address these issues.

Products developed to treat diseases caused by or to combat the threat of bioterrorism or biowarfare will be subject to changing political and social environments. The political and social responses to bioterrorism and biowarfare have been unpredictable and much debated. Changes in the perception of the risk that military personnel or civilians could be exposed to biological agents as weapons of bioterrorism or biowarfare may delay or cause resistance to bringing our products to market or limit pricing or purchases of our products, any of which could materially harm our business.

In addition, substantial delays or cancellations of purchases could result from protests or challenges from third parties, including potential lawsuits brought against us by third parties such as activists. Even if not successful, such protests and litigation require us to spend time and money defending the value of our product or contracts. The need to address political and social issues may divert our management’s time, attention and resources from other business concerns.

Additional lawsuits, publicity campaigns or other negative publicity may adversely affect the degree of market acceptance of, and thereby limit the demand for, TPOXX^® and our biodefense product candidates. In such event, our ability to market and sell such products may be hindered and the commercial success of TPOXX^® and other products we develop may be harmed, thereby reducing our revenues.

Risks Related to Product Development

Our business depends significantly on our success in completing development and commercialization of drug candidates that are still under development. If we are unable to commercialize these drug candidates, or experience significant delays in doing so, our business will be materially harmed.

We have invested a substantial majority of our efforts and financial resources in the development of our drug candidates. Our ability to generate near-term cash-flows is primarily dependent on the success of our smallpox antiviral drug candidate TPOXX^®. The commercial success of our drug candidates will depend on many factors, including:

We expect to rely on FDA regulations known as the “animal rule” to obtain approval for certain of our biodefense drug candidates. The animal rule permits the use of animal efficacy studies together with human clinical safety trials to support an application for marketing approval. These regulations are relatively new, and both we and the government have limited experience in the application of these rules to the drug candidates that we are developing. It is possible that results from these animal efficacy studies may not be predictive of the actual efficacy of our drug candidates in humans. If we are not successful in completing the development and commercialization of our drug candidates, whether due to our efforts or due to concerns raised by our governmental regulators or customers, our business could be materially harmed.

We will not be able to commercialize our drug candidates if our pre-clinical development efforts are not successful, our clinical trials do not demonstrate safety or our clinical trials or animal studies do not demonstrate efficacy.

Before obtaining regulatory approval for the sale of our drug candidates, we must conduct extensive pre-clinical development, trials to demonstrate the safety of our drug candidates and clinical or animal trials to demonstrate the efficacy of our drug candidates. Pre-clinical and clinical testing is expensive, difficult to design and implement, can take many years to complete and is uncertain as to outcome. Success in pre-clinical testing and early clinical trials does not ensure that later clinical trials or animal efficacy studies will be successful, and interim results of a clinical trial or animal efficacy study do not necessarily predict final results.

A failure of one or more of our clinical trials or animal efficacy studies can occur at any stage of development. We may experience numerous unforeseen events during, or as a result of, pre-clinical testing and the clinical trial or animal efficacy study process that could delay or prevent our ability to receive regulatory approval or commercialize our drug candidates, including:

We are in various stages of product development and there can be no assurance of successful commercialization.

In general, our research and development programs are at various stages of development, with some candidates at an early stage of development. To obtain FDA approval for our biodefense products, we will be required to obtain adequate proof of efficacy from multiple animal model studies and provide animal and human safety data. Our other products will be subject to the usual FDA regulatory requirements, which include a number of phases of testing in humans.

FDA has not approved any of our biopharmaceutical product candidates. Any drug candidate we develop will require significant additional research and development efforts, including extensive pre-clinical and clinical testing and regulatory approval, prior to commercial sale. We cannot be sure our approach to drug discovery will be effective or will result in the successful commercialization of any drug. We cannot predict with certainty whether any drug resulting from our research and development efforts will be commercially available within the next several years, or if they will be available at all.

Even if we receive initially positive pre-clinical or clinical results, such results do not mean that similar results will be obtained in later stages of drug development, such as additional pre-clinical testing or human clinical trials. All of our potential drug candidates are prone to the risks of failure inherent in pharmaceutical product development, including the possibility that none of our drug candidates will or can:

In addition, third parties may preclude us from marketing our drugs through enforcement of their proprietary or intellectual property rights that we are not aware of, or third parties may succeed in marketing equivalent or superior drug products. Our failure to develop safe, commercially viable drugs would have a material adverse effect on our business, financial condition and results of operations.

Risks Related to Commercialization

Our ability to grow our business depends significantly on our ability to achieve sales of TPOXX^® to customers other than the U.S. government.

An element of our business strategy is to sell TPOXX^® to customers other than the U.S. government. These potential customers include foreign governments and state and local governments, as well as non-governmental organizations focused on global health like the World Health Organization, health care institutions like hospitals (domestic and foreign) and certain large business organizations interested in protecting their employees against global threats.

The market for sales of TPOXX^® to customers other than the U.S. government is undeveloped, and we may not be successful in generating meaningful sales of TPOXX^®, if any, to these potential customers.

Governmental regulations may make it difficult for us to achieve significant sales of TPOXX^® to customers other than the U.S. government. For example, federal and foreign regulations usually require approval of the drug under generally applicable food and drug laws or waivers of such approval before these customers may procure the drug. Additionally, federal laws place various restrictions on the export of drugs that are not FDA-approved or that have potential biodefense-related uses. These restrictions are subject to change as global conditions change. These restrictions and other regulations on drug sales could limit our sales of TPOXX^® to foreign governments and other commercial or foreign customers. In addition, U.S. government demand for TPOXX^® may limit supplies of TPOXX^® available for sale to non-U.S. government customers.

If we fail to increase our sales of TPOXX^® to customers other than the U.S. government, our business and opportunities for growth could be materially limited.

Because we must obtain regulatory clearance or otherwise operate under strict legal requirements in order to test and market our products in the U.S., we cannot predict whether or when we will be permitted to commercialize our products other than through the BARDA Contract.

Except with respect to sales to BARDA under Project BioShield, pharmaceutical products cannot generally be marketed in the U.S. until they have has completed rigorous pre-clinical testing and clinical trials and an extensive regulatory clearance and approval process implemented by FDA. Pharmaceutical products typically take many years to satisfy regulatory requirements and require the expenditure of substantial resources depending on the type, complexity and novelty of the product and its intended use.

Before commencing clinical trials in humans, we must submit and receive clearance from FDA through a process begun by an IND application. Institutional review boards and FDA oversee clinical trials. Such trials:

Before receiving FDA clearance to market a product in the absence of a medical or public health emergency, we must demonstrate that the product is safe and effective on the patient population that will be treated. Data we obtain from pre-clinical and clinical activities and from animal models are susceptible to varying interpretations that could delay, limit or prevent regulatory clearances. Additionally, conducting and managing pre-clinical and clinical trials and animal efficacy studies and manufacturing processes necessary to obtain regulatory approval always involves some risk.

If full regulatory clearance of a product is granted, this clearance will be limited only to those conditions for which the product is demonstrated through clinical trials to be safe and efficacious. We cannot ensure that any compound developed by us, alone or with others, will prove to be safe and efficacious in pre-clinical or clinical trials or animal efficacy studies and will meet all of the applicable regulatory requirements needed to receive full marketing clearance.

The biopharmaceutical market in which we compete and will compete is highly competitive.

The biopharmaceutical industry is characterized by rapid and significant technological change. Our success will depend on our ability to develop and apply our technologies in the design and development of our product candidates and to establish and maintain a market for our product candidates. In addition, there are many companies, both public and private, including major pharmaceutical and chemical companies, specialized biotechnology firms, universities and other research institutions engaged in developing pharmaceutical and biotechnology products. Many of these companies have substantially greater financial, technical, research and development resources, and human resources than us. Competitors may develop products or other technologies that are more effective than any that are being developed by us or may obtain FDA approval for products more rapidly than us. If we commence commercial sales of products, we still must compete in the manufacturing and marketing of such products, areas in which it is very difficult to succeed and in which we have limited experience. Many potential competitors have manufacturing facilities and established marketing capabilities that would enable such companies to market competing products through existing channels of distribution which could provide a substantial advantage.

Our potential products may not be acceptable in the market or eligible for third-party reimbursement resulting in a negative impact on our future financial results.

Any product we develop may not achieve market acceptance. The degree of market acceptance of any of our products will depend on a number of factors, including:

Physicians, patients or the medical community in general may not accept or utilize any product we may develop. Our ability to generate revenues and income with respect to drugs, if any, developed through the use of our technology will depend, in part, upon the extent to which payment or reimbursement for the cost of such drugs will be available from third-party payors, such as governmental suppliers like BARDA, CDC or DoD, governmental health administration authorities, private healthcare insurers, health maintenance organizations, pharmacy benefits management companies and other organizations. Third-party payors are increasingly disputing the prices charged for pharmaceutical products. If third-party payment or reimbursement was not available or sufficient to allow profitable price levels to be maintained for drugs we develop, it could adversely affect our business.

Product liability lawsuits could cause us to incur substantial liabilities and require us to limit commercialization of any products that we may develop.

We face an inherent business risk related to the sale of TPOXX^® and any other products that we successfully develop and the testing of our product candidates in clinical trials.

TPOXX^® is currently identified as a covered countermeasure under a Public Readiness and Emergency Preparedness Act (the “PREP Act”) declaration issued in October 2008, as amended, which provides us with substantial immunity with respect to the manufacture, administration or use of TPOXX^®. Under our BARDA Contract, the U.S. government should indemnify us against claims by third parties for death, personal injury and other damages related to TPOXX^®, including reasonable litigation and settlement costs, to the extent that the claim or loss results from specified risks not covered by insurance or caused by our grossly negligent or criminal behavior. The collection process can be lengthy and complicated, and there is no guarantee that we will be able to recover these amounts from the U.S. government.

If we cannot successfully defend ourselves against future claims that our product or product candidates caused injuries and we are not entitled to or able to obtain indemnity by the U.S. government with respect to such claims, or if the U.S. government does not honor its indemnification obligations, we may incur substantial liabilities. Regardless of merit or eventual outcome, product liability claims may result in:

We currently have product liability insurance with coverage up to a $10 million annual aggregate limit and up to $10 million per occurrence. The amount of insurance that we currently hold may not be adequate to cover all liabilities that may occur. Product liability insurance is difficult to obtain and increasingly expensive. We may not be able to maintain insurance coverage at a reasonable cost and we may not be able to maintain or obtain insurance coverage that will be adequate to satisfy any liability that may arise.

Additionally, a successful product liability claim or series of claims brought against us could cause our stock price to fall, could decrease our financial resources and materially, exhaust our existing insurance or limit our ability to obtain insurance going forward, all of which would adversely affect our business.

We may be required to perform additional clinical trials or change the labeling of our products if we or others identify side effects after our products are on the market, which could harm future sales of the affected products.

If we or others identify side effects after any of our products are on the market, or if manufacturing problems occur:

Any of the above occurrences could harm or prevent future sales of the affected products or could increase the costs and expenses of commercializing and marketing these products.

Healthcare reform and controls on healthcare spending may limit the price we charge for our products and the amounts that we can sell.

There have been a number of legislative and regulatory proposals in the United States to change the health care system in ways that could affect our ability to sell our products profitably. One enacted proposal, the Patient Protection and Affordable Care Act, as amended by the Health Care and Education Reconciliation Act of 2010 (collectively, the “Healthcare Reform Act”), substantially changes the way healthcare is financed by both governmental and private insurers and will have a substantial effect on the pharmaceutical industry. The Healthcare Reform Act contains a number of provisions, including those governing enrollment in federal healthcare programs like Medicare, reimbursement changes and rules protecting against fraud and abuse, that will change existing healthcare programs and will result in the development of new programs, including Medicare payment for performance initiatives and improvements to the physician quality reporting system and feedback program. We anticipate that, if we obtain marketing approval for our products, some of our revenue may be derived from governmental healthcare programs, including Medicare. Furthermore, beginning in 2011, the Healthcare Reform Act imposed a non-deductible excise tax on pharmaceutical manufacturers or importers who sell “branded prescription drugs,” which includes innovator drugs and biologics (excluding orphan drugs or generics) to U.S. government programs. The Healthcare Reform Act and other healthcare reform measures that may be adopted in the future could have an adverse effect on our industry generally and potential future sales and profitability of our products specifically.

Laws and regulations governing international operations may preclude us from developing, manufacturing and selling certain product candidates outside of the United States and require us to revise and implement costly compliance programs.

If we expand our operations outside of the United States, we must comply with numerous laws and regulations relating to our business operations in each jurisdiction in which we plan to operate. The creation and implementation of international business practices and compliance programs is costly and such programs can be difficult to enforce, particularly where reliance on third parties is required.

The Foreign Corrupt Practices Act, or FCPA, prohibits any U.S. individual or business from paying, offering, or authorizing payment or offering of anything of value, directly or indirectly, to any foreign official, political party or candidate for the purpose of influencing any act or decision of the foreign entity in order to assist the individual or business in obtaining or retaining business. The FCPA also obligates companies whose securities are listed in the United States to comply with certain accounting provisions requiring the Company to maintain books and records that accurately and fairly reflect all transactions of the corporation, including international subsidiaries, and to devise and maintain an adequate system of internal accounting controls for international operations. The anti-bribery provisions of the FCPA are enforced primarily by the U.S. Department of Justice. The SEC is involved with enforcement of the books and records provisions of the FCPA.

Compliance with the FCPA is expensive and can be difficult, particularly in countries in which corruption is a recognized problem. In addition, the FCPA presents particular challenges in the pharmaceutical industry, because, in many countries, hospitals are operated by the government, and doctors and other hospital employees are considered foreign officials. Certain payments to hospitals in connection with clinical studies and other work have been deemed to be improper payments to government officials and have led to FCPA enforcement actions. In addition, biodefense companies like SIGA often sell their products directly to foreign governments.

Various laws, regulations and executive orders also restrict the use and dissemination outside of the United States, or the sharing with certain non-U.S. nationals, of information classified for national security purposes, as well as certain products and technical data relating to those products. If we expand our presence outside of the United States, it will require us to dedicate additional resources to compliance with these laws, and these laws may preclude us from developing, manufacturing, or selling certain products and product candidates outside of the United States, which could limit our growth potential and increase our development costs.

The failure to comply with laws governing international business practices may result in substantial penalties, including suspension or debarment from government contracting. Violation of the FCPA can result in significant civil and criminal penalties that can be levied on the Company and its executives.

Indictment alone under the FCPA can lead to suspension of the right to do business with the U.S. government until the pending claims are resolved. Conviction of a violation of the FCPA can result in long-term disqualification

as a government contractor. The termination of a government contract or relationship as a result of our failure to satisfy any of our obligations under laws governing international business practices would have a material negative impact on our operations and harm our reputation and ability to procure government contracts. The SEC also may suspend or bar issuers from trading securities on United States exchanges for violations of the FCPA’s accounting provisions.

Other countries such as the UK have anti-bribery laws similar to or more expansive in scope than the FCPA which may be applicable to our operations.

If we are unable to expand our internal sales and marketing capabilities or enter into agreements with third parties, we may be unable to generate cash flows from product sales to customers other than the U.S. government.

To achieve commercial success for any approved product, we may need to enhance our own sales and marketing capabilities, enter into collaborations with third parties able to perform these services or outsource these functions to third parties.

We currently employ a small, targeted group to support development and business activities related to TPOXX^®. We plan to continue to do so and expect that we will use a similar approach for sales to the U.S. government of any other biodefense product candidates that we successfully develop. If we are unable to adequately support our development and business activities, we may be unable to expand our sales of TPOXX^®, which could have an adverse effect on our growth.

Risks Related to Manufacturing and Manufacturing Facilities

Problems related to large-scale commercial manufacturing could cause us to delay product launches or experience shortages of products.

Manufacturing drug products, especially in large quantities, is complex. Our drug candidates require several manufacturing steps at multiple facilities, and may involve complex techniques to assure quality and sufficient quantity, especially as the manufacturing scale increases. Our products must be made consistently and in compliance with a clearly defined manufacturing process. Accordingly, it is essential to be able to validate and control the manufacturing process to assure that it is reproducible. Slight deviations anywhere in the manufacturing process, including obtaining materials, filling, labeling, packaging, storage, shipping, quality control and testing, some of which all pharmaceutical companies, including SIGA, experience from time to time, may result in lot failures, delay in the release of lots, product recalls or spoilage. Success rates can vary dramatically at different stages of the manufacturing process, which can lower yields and increase costs. We may experience deviations in the manufacturing process that may take significant time and resources to resolve and, if unresolved, may affect manufacturing output and/or cause us to fail to satisfy contractual commitments, lead to delays in our clinical trials or result in litigation or regulatory action.

If third parties do not manufacture our drug candidates or products in sufficient quantities and at an acceptable cost or in compliance with regulatory requirements and specifications, the development and commercialization of our drug candidates could be delayed, prevented or impaired.

We currently rely on third parties to manufacture drug candidates that we require for pre-clinical and clinical development, including TPOXX^®. Any significant delay in obtaining adequate supplies of our drug candidates could adversely affect our ability to develop or commercialize these drug candidates. We expect that we will rely on third parties for a portion of the manufacturing process for commercial supplies of drug candidates that we successfully develop. If our contract manufacturers are unable to scale-up production to generate enough materials for commercial launch, the success of those products may be jeopardized. Our current and anticipated future dependence upon others for the manufacture of our drug candidates may adversely affect our ability to develop drug candidates and commercialize any product that receives regulatory approval on a timely and competitive basis. If our third party manufacturers’ production processes malfunction or contaminate our drug supplies during manufacturing, we may incur significant inventory loss that may not be covered by our contractual provisions or insurance policies.

We currently rely on third parties to demonstrate regulatory compliance and for quality assurance with respect to the drug candidates manufactured for us. We intend to continue to rely on these third parties for these purposes with respect to production of commercial supplies of drugs that we successfully develop. Manufacturers are subject to ongoing, periodic, unannounced inspection by FDA and corresponding state and foreign agencies or their designees to ensure strict compliance with applicable laws and regulations.

We cannot be certain that our present or future manufacturers will be able to comply with these regulations and other FDA regulatory requirements or similar regulatory requirements outside the U.S. Our contracts and grants call for compliance with all applicable legal and regulatory requirements, however, we do not control third-party manufacturers and their methods for ensuring adherence to regulatory and legal standards. If we or these third parties fail to comply with applicable regulations, sanctions could be imposed on us which could significantly delay and adversely affect supplies of our drug candidates.

Our activities may involve hazardous materials, use of which may subject us to environmental regulatory liabilities.

Our biopharmaceutical research and development sometimes involves the use of hazardous and radioactive materials and generation of biological waste. We are subject to federal, state and local laws and regulations governing the use, manufacture, storage, handling and disposal of these materials and certain waste products. Although we believe that our safety procedures for handling and disposing of these materials comply with legally prescribed standards, the risk of accidental contamination or injury from these materials cannot be completely eliminated. In the event of an accident, we could be held liable for damages, and this liability could exceed our resources. We use, for example, small amounts of radioactive isotopes commonly used in pharmaceutical research, which are stored, used and disposed of in accordance with Nuclear Regulatory Commission regulations. Our general liability policy provides coverage up to annual aggregate limits of $2 million and coverage of $2 million per occurrence.

We believe that we are in compliance in all material respects with applicable environmental laws and regulations and currently do not expect to make material additional capital expenditures for environmental control facilities in the near term. However, we may have to incur significant costs to comply with current or future environmental laws and regulations.

Risks Related to Sales of Biodefense Products to the U.S. Government

Our business could be adversely affected by a negative audit by the U.S. government.

U.S. government agencies such as the Defense Contract Audit Agency (the “DCAA”), routinely audit and investigate government contractors. These agencies review a contractor’s performance under its contracts and grants, cost structure, and compliance with applicable laws, regulations and standards.

The DCAA also reviews the adequacy of, and a contractor’s compliance with, its internal control systems and policies, including the contractor’s purchasing, property, estimating, compensation and management information systems. Any cost found to be improperly allocated to a specific contract will not be reimbursed, while such costs already reimbursed must be refunded. If an audit uncovers improper or illegal activities, we may be subject to civil and criminal penalties and administrative sanctions, including:

Laws and regulations affecting government contracts and grants might make it more costly and difficult for us to conduct our business.

We must comply with numerous laws and regulations relating to the formation, administration and performance of government contracts and grants, which can make it more difficult for us to retain our rights under these contracts. These laws and regulations affect how we do business with federal, state and local governmental agencies. Among the most significant government contracting regulations that affect our business are:

former government employees, restrict the granting of gratuities and funding of lobbying activities and incorporate other requirements such as the Anti-Kickback Act and the FCPA;

Risks Related to Regulatory Approvals

If we are not able to obtain required regulatory approvals, we will not be able to commercialize our drug candidates in the United States other than through sales to BARDA, and our ability to generate revenue will be materially impaired.

Our drug candidates and the activities associated with their development and commercialization, including their testing, manufacture, safety, efficacy, recordkeeping, labeling, storage, approval, advertising, promotion, sale and distribution, are subject to comprehensive regulation by FDA and other regulatory agencies in the United States and by comparable authorities in other countries. Failure to obtain regulatory approval for a drug candidate will prevent us from commercializing the drug candidate in the United States other than through sales to BARDA under Project BioShield. We have limited experience in preparing, filing and prosecuting the applications necessary to gain regulatory approvals and expect to rely on third-party contract research organizations and consultants to assist us in this process. Securing FDA approval requires the submission to FDA of extensive pre-clinical and clinical data, animal efficacy studies, information about product manufacturing processes and inspection of facilities and supporting information in order to establish the drug candidate’s safety and efficacy. Our future products may not be effective, may be only moderately effective, or may prove to have significant side effects, toxicities, or other characteristics that may preclude our obtaining regulatory approval or prevent or limit commercial use.

Failure to obtain regulatory approval in international jurisdictions could prevent us from marketing our products abroad.

We intend to seek to market our products outside the United States. To market our products in the European Union and many other foreign jurisdictions, we may need to obtain separate regulatory approvals and comply with numerous and varying regulatory requirements. The approval procedure varies among countries and can involve additional testing. The time required to obtain approval may differ from that required to obtain FDA approval.

The foreign regulatory approval process may include all of the risks associated with obtaining FDA approval. We may not obtain foreign regulatory approvals on a timely basis, if at all. Approval by FDA does not ensure approval by regulatory authorities in other countries or jurisdictions, and approval by one foreign regulatory authority does not ensure approval by regulatory authorities in other foreign countries or jurisdictions or by FDA. We may not be able to file for regulatory approvals and may not receive necessary approvals to commercialize our products in any market.

The Fast Track designation for TPOXX^® may not actually lead to a faster development or regulatory review or approval process.

We have obtained a “Fast Track” designation from FDA for TPOXX^®. However, we may not experience a faster development process, review or approval compared to conventional FDA procedures. FDA may withdraw our Fast Track designation if it believes that the designation is no longer supported by data from our clinical development program. Our Fast Track designation does not guarantee that we will qualify for or be able to take advantage of FDA’s expedited review procedures or that any application that we may submit to FDA for regulatory approval will be accepted for filing or ultimately approved.

Risks Related to Our Dependence on Third Parties

If third parties on whom we rely for clinical trials or certain animal trials do not perform as contractually required or as we expect, we may not be able to obtain regulatory approval for or commercialize our drug candidates and our business may suffer.

We do not have the ability independently to conduct the clinical trials, and certain animal trials, required to obtain regulatory approval for our products. We depend on independent investigators, contract research organizations and other third-party service providers to conduct trials of our drug candidates and expect to continue to do so. We

rely heavily on these third parties for successful execution of our trials, but do not exercise day-to-day control over their activities. We are responsible for ensuring that each of our trials is conducted in accordance with the general investigational plan and protocols for the trial. Moreover, FDA requires us to comply with standards, commonly referred to as Good Clinical Practices, for conducting and recording and reporting the results of clinical trials to assure that data and reported results are credible and accurate and that the rights, integrity and confidentiality of trial participants are protected. Similarly, animal trials are required to comply with Good Laboratory Practices.

We also currently rely on third-party manufacturers and service providers to produce TPOXX^®. Under the BARDA Contract, we are responsible for the performance of these third-party contracts, and our contracts with these third parties give us certain supervisory and quality control rights, but we do not exercise complete day-to-day control over their activities.

Our reliance on third parties that we do not control does not relieve us of the responsibilities and requirements imposed by the BARDA Contract. Third parties may not complete activities on schedule, or may not conduct our trials in accordance with regulatory requirements or our stated protocols. The failure of these third parties to carry out their obligations could delay or prevent the development, approval and commercialization of our drug candidates.

Risks Related to Our Intellectual Property

Our ability to compete may decrease if we do not adequately protect our intellectual property rights.

Our commercial success will depend in part on our ability to obtain and maintain patent protection for our proprietary technologies, drug targets and potential products and to preserve our trade secrets and trademark rights. Because of the substantial length of time and expense associated with bringing potential products through the development and regulatory clearance processes to reach the marketplace, the pharmaceutical industry places considerable importance on obtaining patent and trade secret protection. The patent positions of pharmaceutical and biotechnology companies can be highly uncertain and involve complex legal and factual questions. No consistent policy regarding the breadth of claims allowed in biotechnology patents has emerged to date. Accordingly, we cannot predict the type and breadth of claims allowed in patents covering our products.

SIGA exclusively owns its key patent portfolio, which relates to its leading drug candidate TPOXX^® (ST-246). As of May 24, 2016, the TPOXX^® patent portfolio has seven patent families consisting of ten U.S. utility patents, fourteen issued foreign patents, one U.S. provisional application, five U.S. utility patent applications, and sixty seven foreign patent applications.

We also rely on trade secrets, know-how, continuing technological innovation and licensing opportunities. In an effort to maintain the confidentiality and ownership of trade secrets and proprietary information, we require our employees, consultants and some collaborators to execute confidentiality and invention assignment agreements upon commencement of a relationship with us. These agreements may not provide meaningful protection for our trade secrets, confidential information or inventions in the event of unauthorized use or disclosure of such information, and adequate remedies may not exist in the event of such unauthorized use or disclosure.

If our technologies are alleged or found to infringe the patents or proprietary rights of others, we may be sued, we may have to pay damages or be barred from pursuing a technology, or we may have to license those rights to or from others on unfavorable terms. Even if we prevail, such litigation may be costly.

Our commercial success will depend significantly on our ability to operate without infringing the patents or proprietary rights of third parties. Our technologies, or the technologies of third parties on which we may depend, may infringe the patents or proprietary rights of others. If there is an adverse outcome in any dispute concerning rights to these technologies, then we could be subject to significant liability, required to license disputed rights from or to other parties and/or required to cease using a technology necessary to carry out our research, development and commercialization activities.

The costs to establish or defend against claims of infringement or interference with patents or other proprietary rights can be expensive and time-consuming, even if the outcome is favorable. An outcome of any patent or proprietary rights administrative proceeding or litigation that is unfavorable to us may have a material adverse effect on us. We could incur substantial costs if we are required to defend ourselves in suits brought by third parties or if we initiate such suits. We may not have sufficient funds or resources in the event of litigation. Additionally, we may not prevail in any such action.

Any dispute resulting from claims based on patents and proprietary rights could result in a significant reduction in the coverage of the patents or proprietary rights owned, optioned by or licensed to us and limit our ability to obtain meaningful protection for our rights. If patents are issued to third parties that contain competitive or conflicting claims, we may be legally prohibited from researching, developing or commercializing potential products or be required to obtain licenses to these patents or to develop or obtain alternative technology. We may be legally prohibited from using technology owned by others, may not be able to obtain any license to the patents or technologies of third parties on acceptable terms, if at all, or may not be able to obtain or develop alternative technologies.

In addition, from time to time, the Company is involved in disputes or legal proceedings arising in the ordinary course of business. Those disputes or legal proceedings can be costly, create distractions for our business, and adversely affect the Company.

Furthermore, like many biopharmaceutical companies, we may from time to time hire scientific personnel formerly employed by other companies involved in one or more areas similar to the activities conducted by us. It is possible that we and/or these individuals may be subject to allegations of trade secret misappropriation or other similar claims as a result of their prior affiliations.

Risks Related to Our Business

The loss of key personnel or our ability to recruit or retain qualified personnel could adversely affect our results of operations.

We rely upon the ability, expertise, judgment, discretion, integrity and good faith of our senior management team. Our success is dependent upon our personnel and our ability to recruit and train high quality employees. We must continue to recruit, retain and motivate management and other employees sufficient to maintain our current business and support our projected growth. The loss of services of any of our key management could have a material adverse effect on our business.

Our future success depends on our ability to retain our chief executive officer and other key executives and to attract, retain and motivate qualified personnel. The loss of the services of any key executive might impede the achievement of our research, development and commercialization objectives. Replacing key employees may be difficult and time-consuming because of the limited number of individuals in our industry with the skills and experiences required to develop, gain regulatory approval of and commercialize our product candidates successfully. We generally do not maintain key person life insurance to cover the loss of any of our employees. Recruiting and retaining qualified scientific personnel, clinical personnel and business development personnel will also be critical to our success. We may not be able to attract and retain these personnel on acceptable terms, if at all, given the competition among numerous pharmaceutical and biotechnology companies for similar personnel. We also experience competition for the hiring of scientific and clinical personnel from other companies, universities and research institutions. In addition, we rely on consultants and advisors, including scientific and clinical advisors, to assist us in formulating our research and development, regulatory and commercialization strategy. Our consultants and advisors may be employed by employers other than us and may have commitments under consulting or advisory contracts with other entities that may limit their availability to us.

We may have difficulty managing our growth.

Potential future growth could place a significant strain on our management and operations. Our ability to manage any future growth will depend upon our ability to broaden our management team and our ability to attract, hire and retain skilled employees. Our success will also depend on the ability of our officers and key employees to continue to implement and improve our operational and other systems and to hire, train and manage our employees.

Our ability to use our net operating loss carryforwards may be limited.

As of December 31, 2015, we had NOLs, of $64.6 million to offset future taxable income. The remaining NOLs expire in various years between 2023 and 2034, if not utilized. Under the provisions of the Internal Revenue Code, substantial changes in our ownership, in certain circumstances, will limit the amount of NOLs that can be utilized annually in the future to offset taxable income. In particular, section 382 of the Internal Revenue Code imposes a limitation on a company’s ability to use NOLs if the company experiences a more-than-50% ownership change over a three-year period. If we are limited in our ability to use our NOLs in future years in which we have taxable income,

we may be required to pay more taxes than if we were able to utilize our NOLs fully. For example, as a result of a previous change in stock ownership, the annual utilization of the NOLs generated in tax years prior to 2004 are subject to limitation. The purchase of shares of our common stock in the rights offering may trigger an ownership change with respect to our stock. In the event that the exercise by a stockholder of the basic subscription right or the over-subscription privilege could, as determined by the Company in its sole discretion, potentially result in a limitation on the Company’s ability to use NOLs we may, but are under no obligation to, reduce the exercise by such stockholder of the basic subscription right and/or the over-subscription privilege to such number of shares of common stock as the Company in its sole discretion shall determine to be advisable in order to preserve the Company’s ability to use NOLs.

USE OF PROCEEDS

Assuming the rights offering is fully subscribed, the net proceeds available to us from the rights offering, after deducting estimated offering expenses of $500,000 payable by us, will be approximately $34.8 million. Proceeds of the rights offering will be used by us, in combination with other sources of liquidity, including the proceeds of the Loan Transaction, to satisfy the portion of the PharmAthene Judgment that has not been satisfied prior to the expiration of the rights offering, which we expect to be approximately $84,000,000, as well as to pay the backstop fee of $1.76 million if such fee is paid in cash.

DETERMINATION OF SUBSCRIPTION PRICE

We recognize that prices of our shares may fluctuate and that trading in our securities may be volatile during the period that the rights offering may be open to our shareholders. As a result, we have elected to establish the subscription price immediately after the close of trading on November 8, 2016, which is the expiration date of the rights offering, at a price per share that will be the lower of $1.50 or 85% of the volume weighted average price during market hours on that date.

In establishing the method of determining the subscription price, the board of directors considered a variety of factors including those listed below:

The subscription price does not necessarily bear any relationship to our past or expected future results of operations, cash flows, current financial condition, or any other established criteria for value. No valuation consultant or investment banker has opined upon the fairness or adequacy of the subscription price. You should not consider the subscription price as an indication of actual value of our company or our common stock. You should not assume or expect that, after the rights offering, our shares of common stock will trade at or above the subscription price in any given time period. The market price of our common stock may decline during or after the rights offering. We cannot assure you that you will be able to sell the shares of our common stock purchased during the rights offering at a price equal to or greater than the subscription price. You should obtain a current price quote for our common stock before exercising your subscription rights and make your own assessment of our business and financial condition, our prospects for the future, and the terms of the rights offering. Once made, all exercises of subscription rights are irrevocable, unless set forth otherwise herein.

DILUTION

Dilution in historical net tangible book value per share represents the difference between the amount per share paid by the purchaser of shares of common stock in the rights offering and the pro forma net tangible book value per share of common stock immediately after the closing of the rights offering. The Company defines “net tangible book value” as an amount equal to total assets less an amount equal to the sum of goodwill and total liabilities.

After giving effect to an assumed issuance of 23,523,195 shares of common stock (based on an assumed subscription price of $1.50 per share, but not including any shares that may be issued in payment of the fee under the backstop agreement), and after deducting estimated offering expenses payable by us of $500,000, our pro forma net tangible book value as of June 30, 2016 would have been approximately ($270,689,315), or ($3.48) per share of common stock. This amount represents an immediate increase of $2.14 per share to our stockholders on shares of common stock owned prior to the rights offering and an immediate dilution of $4.98 per share from the price of $1.50 per share on shares of common stock purchased in the rights offering. Our pro forma net tangible book value per share as of June 30, 2016 is determined using 77,807,491 shares outstanding as of June 30, 2016, which assumes the issuance of 23,523,195 shares of our common stock.

The pro forma dilution in net tangible book value per share to purchasers set forth above is illustrative only and will be adjusted based on the actual subscription price. For purposes of the above calculations we have assumed a subscription price of $1.50; the actual subscription price will be the lower of $1.50 or 85% of the actual volume weighted average price per share of our common stock during market hours on the OTC Pink Sheets on the expiration date, and thus could be materially different from the price utilized below as a result of future changes in the market price of our common stock. Additionally, for the purposes of the above calculations, any shares that may be issued in payment of the fee under the backstop agreement have not been included. You should read this information in conjunction with our consolidated financial statements and notes thereto incorporated by reference into this prospectus.

CAPITALIZATION

The following table sets forth our historical and pro forma cash and cash equivalents and capitalization as of June 30, 2016. The pro forma information gives effect to:

This table should be read in conjunction with our consolidated financial statements and the notes thereto included in this prospectus.

The pro forma as adjusted information set forth above is illustrative only and will be adjusted based on the subscription price. For purposes of the table above we have assumed a subscription price of $1.50; the actual subscription price will be the lower of $1.50 or 85% of the actual volume weighted average price per share of our common stock during market hours on the OTC Pink Sheets on the expiration date, and thus could be materially different from the price utilized below as a result of future changes in the market price of our common stock. You should read this information in conjunction with our consolidated financial statements and notes thereto incorporated by reference into this prospectus.

PRICE RANGE OF COMMON STOCK AND DIVIDEND POLICY

Since March 20, 2015, the Company’s common stock had been traded on the OTC Pink Sheets. The Company’s common stock traded under the symbol “SIGAQ” from March 20, 2015 until April 17, 2016, and since April 18, 2016, it has traded under the symbol “SIGA.” Prior to March 20, 2015, the Company’s common stock had been traded on the Nasdaq Global Market under the symbol “SIGA” since September 3, 2009 and, prior to such date, had been traded on the Nasdaq Capital Market since September 9, 1997. Prior to that time there was no public market for our common stock.

The Company trades on the OTC Pink Sheets because, due to the Company’s chapter 11 filing, the Company no longer met the continuing listing requirements necessary to maintain its listing on the Nasdaq Global Market and Nasdaq suspended from trading the Company’s common stock at the open of business on March 20, 2015.

The following table sets forth, for the periods indicated, the high and low sales prices for the common stock, as reported on the Nasdaq Global Market and the OTC Pink Sheets, as applicable:

As of October 20, 2016, the closing sale price of our common stock was $2.60 per share. There were 29 holders of record as of October 12, 2016. We believe that the number of beneficial owners of our common stock is substantially greater than the number of record holders, because a large portion of common stock is held in broker “street names.”

We have paid no dividends on our common stock and do not expect to pay cash dividends in the foreseeable future. The Plan restricts our ability to declare, set aside or pay any dividend or other distribution (whether in cash, securities or property) with respect to its capital stock or other equity interests or rights, other than as set forth in employment agreements and/or a management incentive plan that, until the PharmAthene Judgment has been satisfied, must be agreed to by the creditor’s committee under the Plan. We currently intend to retain any future earnings to finance the growth and development of our business and to satisfy creditor claims in connection with the chapter 11 case.

THE RIGHTS OFFERING

Background of the Rights Offering

We are distributing to holders of our common stock, at no charge, non-transferable subscription rights to purchase shares of our common stock. We refer to the offering that is the subject of this prospectus as the rights offering. In the rights offering, you will receive the right to invest $0.65 for each share of common stock owned at 5:00 p.m., New York City Time, on October 12, 2016, the record date of the rights offering. The subscription rights will not be tradable. The price per share will be determined on November 8, 2016, which is the expiration date of the rights offering, and will equal the lower of $1.50 or 85% of the volume weighted average price of our shares during market hours as reported on the OTC Pink Sheets on the expiration date. We refer to the price as so determined as the subscription price. We determined the investment amount of $0.65 per basic subscription right by dividing the amount of gross proceeds we wish to raise for the purposes described herein in “Use of Proceeds” ($35,284,792) by the number of rights we are distributing in the rights offering (54,284,296).

Each subscription right will entitle you to invest $0.65 towards the purchase of shares of our common stock, which we refer to as the basic subscription right, at the subscription price. If you exercise your basic subscription rights in full, and other shareholders do not fully exercise their basic subscription rights, you will be entitled to an over-subscription privilege to purchase a portion of the unsubscribed Common Stock at the subscription price, subject to proration and ownership limitations, which we refer to as the over-subscription privilege. Each subscription right consists of a basic subscription right and an over-subscription privilege. The number of shares that you will obtain will equal the accepted dollar amount of your investment divided by the subscription price rounded down to the nearest whole share. If all the subscription rights were exercised, the total gross proceeds to us from the sale of shares of common stock offered in the rights offering would be approximately $35.3 million. The net proceeds of the rights offering, after deducting estimated offering expenses of $500,000, will be approximately $34.8 million. Proceeds of the rights offering will be used by us, in combination with other sources of liquidity, to satisfy the PharmAthene Judgment.

Simultaneous Loan Transaction

Loan Agreement

On September 2, 2016, we entered into a loan and security agreement (the “Loan Agreement”) with OCM Strategic Credit SIGTEC Holdings, LLC, in its capacity as a lender thereunder and each other party who is or thereafter becomes a party to the Loan Agreement as a lender (collectively the “Lenders”, and each individually, a “Lender”), Cortland Capital Market Services LLC, in its capacity as administrative agent for the Lenders and collateral agent for the Secured Parties (as defined in the Loan Agreement) (together with its successors and assigns in such capacity, the “Agent”), OCM Strategic Credit SIGTEC Holdings, LLC, as sole lead arranger, and each of the other persons who are or thereafter become parties to the Loan Agreement as guarantors. The Loan Agreement provides for a first-priority senior secured term loan facility in the aggregate principal amount of $80,000,000 (the “Term Loan”), of which (i) $25,000,000 (net of any interest owed under the Loan Agreement accrued and unpaid and owing as of the Escrow Release Date (as defined below)) of such Term Loan will be held in a reserve account (the “Reserve Account”); (ii) an additional $5,000,000 will also be held in the Reserve Account and up to the full amount of such $5,000,000 may be withdrawn after June 30, 2018 upon the satisfaction of certain conditions as more particularly described in the Loan Agreement, provided that any of such amount is required to fund any interest to the extent any interest in excess of $25,000,000 is due and owing and any of such $5,000,000 remains in the Reserve Account; and (iii) $50,000,000 (net of fees and expenses then due and owing to the Agent or any Lender) of such Term Loan will be paid to PharmAthene or its designee as part of a final payment to satisfy the PharmAthene Judgment. $25,000,000 of the funds held in the aforementioned Reserve Account will be utilized to pay interest on the Term Loan as it becomes due. Funds from the Term Loan can only be released from escrow and used as part of a final payment to satisfy the PharmAthene Judgment once the Company completes the rights offering, and provided that the PharmAthene Judgment is fully satisfied upon the Escrow Release Date and certain other conditions as more particularly described in the Loan Agreement are satisfied. Until these conditions are met, funds from the Term Loan are not available for use by the Company. Until the Escrow Release Date occurs, no security shall be granted under the Loan Agreement and no affirmative or negative covenants or events of default shall be effective under the Loan Agreement.

The Term Loan will initially be held in an escrow account. The Term Loan bears interest from the date on which any of the Term Loan is first placed into such escrow account (the “Escrow Funding Date”) until such Term Loan

is fully repaid at a rate per annum equal to the Adjusted LIBO Rate (as defined in the Loan Agreement) plus 11.50%, subject to adjustment as set forth in the Loan Agreement. The Escrow Funding Date was September 30, 2016. Upon satisfaction of certain conditions as more particularly described in the Loan Agreement, including, but not limited to, concurrent final payment and satisfaction in full of the PharmAthene Judgment, $30,000,000 (net of any interest owed under the Loan Agreement as of the Escrow Release Date) will be transferred from the escrow account to the Reserve Account (the date on which such transfer occurs, the “Escrow Release Date”).

The Term Loan shall mature on the earliest to occur of (i) the four year anniversary of the Escrow Release Date, (ii) the acceleration of certain obligations pursuant to the Loan Agreement, and (iii) December 1, 2016 if certain conditions as more particularly described in the Loan Agreement, such as final payment of the PharmAthene Judgment, are not satisfied by November 30, 2016.

Through the three and one-half year anniversary of the Escrow Release Date, any prepayment of the Term Loan is subject to a make-whole in which interest payments related to the prepaid amount are due (subject to a discount of treasury rate plus 0.50%).

Upon any partial or full prepayment or repayment of the Term Loan, an exit fee will be payable equal to 5.00% of the principal amount of any partial or full prepayment or repayment.

In connection with the Term Loan, the Company has granted to the Agent, for the benefit of the Secured Parties, a lien on and security interest in all of the Company’s right, title and interest in substantially all of the Company’s tangible and intangible assets, including all intellectual property.

The Loan Agreement contains customary representations and warranties and customary affirmative and negative covenants. These covenants, among other things, require a minimum cash balance throughout the term of the Term Loan and the achievement of regulatory milestones by certain dates, and contain certain limitations on the ability of the Company to incur unreimbursed research and development expenditures over a certain threshold, make capital expenditures over a certain threshold, incur indebtedness, dispose of assets outside of the ordinary course of business and enter into certain merger or consolidation transactions.

The Loan Agreement includes customary events of default, including, among others: (i) non-payment of amounts due thereunder, (ii) the material inaccuracy of representations or warranties made thereunder, (iii) non-compliance with covenants thereunder, (iv) non-payment of amounts due under, or the acceleration of, other material indebtedness of the Company and (v) bankruptcy or insolvency events. Upon the occurrence and during the continuance of an event of default under the Loan Agreement, the interest rate may increase by 2.00% per annum above the rate of interest otherwise in effect, and the Lenders would be entitled to accelerate the maturity of the Company’s outstanding obligations thereunder.

Warrant

In connection with the entry into the Loan Agreement, the Company issued a Warrant to OCM Strategic Credit SIGTEC Holdings, LLC to purchase a number of shares of the Company’s common stock equal to $4,000,000 divided by the lower of (i) $2.29 per share and (ii) the subscription price paid in connection with the rights offering (the “Warrant”). The Warrant provides for weighted average anti-dilution protection and is exercisable in whole or in part for ten (10) years from the date of issuance.

Completion of the rights offering is conditioned on the closing of the Loan Transaction, which we expect to be consummated simultaneously with the completion of the rights offering. Funds received in payment of the subscription price are anticipated to be held in escrow until each of the Loan Transaction and the rights offering are consummated, or until the Company definitively determines to terminate the rights offering. If the Loan Transaction does not close by November 30, 2016, we will terminate the rights offering and returning any subscription payments received from our rights holders, without interest or penalty. Any funds held in escrow pursuant to the Loan Agreement will not be released from escrow to or for use by the Company, whether for satisfaction of the PharmAthene Judgment or for any other purpose, unless the Company consummates the rights offering. Neither the rights offering nor the Loan Transaction will be consummated unless the Company determines in its sole discretion that, upon consummation of both the rights offering and the Loan Transaction (or through some other source of financing), the Company will have sufficient cash to fully satisfy the PharmAthene Judgment.

Basic Subscription Rights

We will distribute to each holder of our common stock who is a record holder of our common stock on the record date, which is October 12, 2016, at no charge, one non-transferable subscription right for each share of common stock owned as of the record date. As of the record date, an aggregate of 54,284,296 shares of our common stock were outstanding.

Your basic subscription rights will entitle you to invest $0.65 towards the purchase of shares of our common stock for each share of stock that you own on the record date, upon timely delivery of the required documents and payment of the subscription price. For example, if you owned 20 shares of Common Stock on the record date, you would receive 20 rights and would have the right to invest $0.65 for each share of Common Stock you own as of the record date at the subscription price. If you have invested $13.00, and if on the expiration date of the rights offering the volume weighted average price of our common stock as reported on the OTC Pink Sheets is $2.50 per share, the subscription price will be $1.50 and you would receive a rounded down 8 shares and a refund of $1.00. If you have invested $13.00 and if on the expiration date of the rights offering the volume weighted average price of our common stock during market hours as reported on the OTC Pink Sheets is $1.60 per share, the subscription price will be $1.36 per share (which constitutes 85% of $1.60), you would receive a rounded down 9 shares and a refund of $0.76.

The subscription rights will be evidenced by non-transferable subscription rights certificates. Any excess payment will be returned to you, as soon as practicable, without interest or penalty. If rights holders wish to exercise their subscription rights, they must do so prior to 5:00 p.m., New York City time, on November 8, 2016, the expiration date for the rights offering, subject to extension by the Company in its sole discretion (provided, however, that the Company may not extend the expiration date of the rights offering past November 29, 2016). After the expiration date, the subscription rights will expire and will have no value. See below under “— Expiration of the Rights Offering; Extensions and Amendments.” You may exercise all or a portion of your basic subscription rights, or you may choose not to exercise any of your basic subscription rights. If you do not exercise your basic subscription rights in full, you will not be entitled to exercise your over-subscription privilege.

Over-Subscription Privilege

If you exercise your basic subscription rights in full, you may also choose to exercise your over-subscription privilege. Subject to proration and limitations on exercise we may impose that are described below in “— Limitations on Exercise,” if applicable, we will seek to honor the over-subscription privilege requests in full. If over-subscription privilege requests exceed the number of shares available, however, we will allocate the available shares pro rata among the record holders exercising the over-subscription privilege in proportion to the number of shares of our common stock each of those record holders owned on the record date, relative to the number of shares owned by all record holders exercising the over-subscription privilege. If this pro rata allocation results in any record holder receiving a greater number of shares than the record holder subscribed for pursuant to the exercise of the over-subscription privilege, then such record holder will be allocated only that number of shares for which the record holder oversubscribed, and the remaining shares will be allocated among all other record holders exercising the over-subscription privilege on the same pro rata basis described above. The proration process will be repeated until all shares have been allocated.

The subscription agent will determine the over-subscription allocation based on the formula described above. To the extent the aggregate subscription payment of the actual number of unsubscribed shares available to you at the subscription price pursuant to the over-subscription privilege is less than the amount you actually paid in connection with the exercise of the over-subscription privilege, you will be allocated, after the subscription price is determined, only the number of unsubscribed shares available to you, and any excess subscription payments will be returned to you, without interest or penalty, as soon as practicable after expiration of the rights offering.

We can provide no assurances that, following determination of the subscription price, you will actually be entitled to purchase the number of shares issuable upon the exercise of your over-subscription privilege in full at the expiration of the rights offering. We will not be able to satisfy any requests for shares pursuant to the over-subscription privilege if all of our stockholders exercise their basic subscription rights in full, and we will only honor an over-subscription privilege to the extent sufficient shares are available following the exercise of basic subscription rights.

Subscription Price

We recognize that prices of our shares may fluctuate and that trading in our securities may be volatile during the period that the rights offering may be open to our shareholders. As a result, we have elected to establish the subscription price immediately after the close of trading on November 8, 2016, which is the expiration date of the rights offering, at a price per share that will be the lower of $1.50 or 85% of the volume weighted average price during market hours on that date. The subscription price as so determined does not necessarily bear any relationship to our past or expected future results of operations, cash flows, current financial condition, or any other established criteria for value.

Limitations on Exercise

In the event that the exercise by a stockholder of the basic subscription right or the over-subscription privilege could, as determined by the Company in its sole discretion, potentially result in a limitation on the Company’s ability to use NOLs under the Code and the rules promulgated thereunder, the Company may, but is under no obligation to, reduce the exercise by such stockholder of the basic subscription right or the over-subscription privilege to such number of shares of common stock as the Company in its sole discretion shall determine to be advisable in order to preserve the Company’s ability to use NOLS.

Expiration of the Rights Offering; Extensions and Amendments

You may exercise your subscription rights at any time prior to 5:00 p.m., New York City time, on November 8, 2016, the expiration date for the rights offering. If you do not exercise your subscription rights before the expiration date of the rights offering, your subscription rights will expire and will have no value. We will not be required to issue any new common stock to you if the subscription agent receives your rights certificate or payment, after the expiration date, regardless of when you sent the rights certificate and payment, unless you send the documents in compliance with the guaranteed delivery procedures described below.

We may, in our sole discretion, extend the time for exercising the subscription rights; provided, however, that we may not extend the expiration date of the rights offering past November 29, 2016. We may extend the expiration date at any time after the record date. If the commencement of the rights offering is delayed for a period of time, the expiration date of the rights offering may be similarly extended. We will extend the duration of the rights offering as required by applicable law, and may choose to extend the duration of the rights offering for any reason. We may extend the expiration date of the rights offering by giving oral or written notice to the subscription agent on or before the scheduled expiration date. If we elect to extend the expiration date of the rights offering, we will publicly announce such extension no later than 9:00 a.m., New York City time, on the next business day after the most recently announced expiration date. We also reserve the right, in our sole discretion, to amend or modify the terms of the rights offering, provided that to the extent we may not waive a condition (as described below under “— Termination; Conditions to the Rights Offering”) we may not amend or modify the terms of the rights offering to eliminate such condition. An amendment or modification to a material offering term, such as the methodology pursuant to which the subscription price will be determined, will require us to return subscription funds consistent with Exchange Act Rule 10b-9.

Termination Rights; Conditions to the Rights Offering

We reserve the right to cancel or terminate the rights offering, in whole or in part, in our sole discretion at any time prior to the completion of the rights offering, for any reason or no reason.

The rights offering is subject to the following conditions:

We may not waive any of the conditions set forth in the first two bullets above.

If we cancel or terminate the rights offering, in whole or in part, all affected subscription rights will expire without value and all funds received in connection with the rights offering will be returned as soon as practicable, without interest or penalty, to those persons who exercised their subscription rights.

Backstop Agreement

In connection with the rights offering, we have entered into an investment agreement, or “backstop agreement,” with the Backstop Parties. Under the terms of the backstop agreement, the Backstop Parties will purchase, pursuant to a separate private placement, a number of shares of common stock equal to the number of shares that are not subscribed for in the rights offering, if any, provided that to the extent MacAndrews’ acquisition of our voting stock would require a filing and approval under the HSR Act, MacAndrews will receive non-voting convertible preferred stock in lieu of common stock, which preferred stock will automatically convert to common stock upon receipt of HSR Act approval, and will not be convertible to common stock without such HSR Act approval. Under the backstop agreement, the subscription price will be equal to the subscription price applicable to all shareholders under the rights offering. The Backstop Parties, taken together, will receive the backstop fee of $1.76 million, or 5% of the maximum gross proceeds of the rights offering, for providing the backstop commitment, payable, at the option of the Company, in cash or stock or, subject to the mutual agreement of the parties, other equity securities.

Representations and Warranties

Under the terms of the backstop agreement, we have made representations and warranties relating to:

The Backstop Parties have made representations and warranties relating to:

Conditions to Closing

Each party’s obligation to consummate the transactions contemplated by the backstop agreement is subject upon the following closing conditions:

Registration Rights

We have agreed that, if we file a shelf registration statement, we will use our reasonable best efforts to include all shares issued pursuant to the backstop agreement (the “Backstop Shares”) in such shelf registration statement.

Indemnification

We have agreed to indemnify the Backstop Parties and their officers, directors, partners, employees, agents and representatives for any losses suffered by such persons resulting from (i) the breach of any representation, warranty or covenant made by us in the backstop agreement or (ii) any untrue or alleged untrue statement of material fact made in a shelf registration statement registering the Backstop Shares (or any other disclosure document produced by or on behalf of the Company) or omission of any material fact required to be stated therein or necessary to make the statements therein not misleading. Each Backstop Party has agreed to indemnify us (severally and not jointly) and our officers and directors for any losses suffered by such persons resulting from any untrue statement of material fact made in a shelf registration statement registering the Backstop Shares or omission of any material fact required to be stated therein or necessary to make the statements therein not misleading (in each case, only to the extent the statement or omission is contained in information provided in writing by such Backstop Party for inclusion in such shelf registration).

Termination of the Backstop Agreement

The backstop agreement is terminable at any time prior to the closing of the rights offering by:

Method of Exercising Subscription Rights

To exercise your subscription rights, you must follow the process described in the subscription documents sent to you and also available from the information agent. For assistance you may contact the information agent, D.F. King & Co., Inc., toll free at 1-800-207-2872, or by email at infoagent@dfking.com.

The exercise of subscription rights is irrevocable and may not be cancelled or modified. Your subscription rights will not be considered exercised unless the subscription agent receives from you, your broker, custodian or nominee, as the case may be, all of the required documents properly completed and executed and your full subscription price payment in cash prior to 5:00 p.m., New York City time, on November 8, 2016, the expiration date of the rights offering. Rights holders may exercise their rights as follows:

Subscription by Registered Holders

Rights holders who are registered holders of our common stock may exercise their subscription privilege by properly completing and executing the rights certificate together with any required signature guarantees and forwarding it, together with payment in full, of the subscription price for the amount of common stock for which they subscribe, to the subscription agent at the address set forth under the subsection entitled “—Delivery of Subscription Materials and Payment,” on or prior to the expiration date.

Subscription by Beneficial Owners

Rights holders who are beneficial owners of shares of our common stock and whose shares are registered in the name of a broker, custodian bank or other nominee and rights holders who hold common stock certificates and would prefer to have an institution conduct the transaction relating to the rights on their behalf, should instruct their broker, custodian bank or other nominee or institution to exercise their rights and deliver all documents and payment on their

behalf, prior to the expiration date. A rights holder’s subscription rights will not be considered exercised unless the subscription agent receives from such rights holder, its broker, custodian, nominee or institution, as the case may be, all of the required documents and such holder’s full subscription price payment.

To properly exercise your over-subscription privilege, you must deliver the subscription payment related to your over-subscription privilege before the rights offering expires. Because we will not know the total number of unsubscribed shares before the rights offering expires, if you wish to maximize the number of shares you purchase pursuant to your over-subscription privilege, you will need to deliver payment in an amount equal to the aggregate subscription payment for the maximum amount that you wish to invest in the rights offering taking into consideration that the number of shares you may acquire will not be fixed until after the rights offering has expired.

Method of Payment

Payments must be made in full in:

Rights certificates received after 5:00 p.m., New York City time, on November 8, 2016, the expiration date of the rights offering, will not be honored, and we will return your payment to you as soon as practicable, without interest or penalty.

The subscription agent will be deemed to receive payment upon:

You should read the instruction letter accompanying the rights certificate carefully and strictly follow it. DO NOT SEND RIGHTS CERTIFICATES OR PAYMENTS TO US. Except as described below under “— Guaranteed Delivery Procedures,” we will not consider your subscription received until the subscription agent has received delivery of a properly completed and duly executed rights certificate and payment of the full subscription amount. The risk of delivery of all documents and payments is on you or your nominee, not us or the subscription agent.

The method of delivery of rights certificates and payment of the subscription amount to the subscription agent will be at the risk of the holders of rights, but, if sent by mail, we recommend that you send those certificates and payments by overnight courier or by registered mail, properly insured, with return receipt requested, and that a sufficient number of days be allowed to ensure delivery to the subscription agent and clearance of payment before the expiration of the subscription period.

Unless a rights certificate provides that the new shares of common stock are to be delivered to the record holder of such rights or such certificate is submitted for the account of a bank or a broker, signatures on such rights certificate must be guaranteed by an “Eligible Guarantor Institution,” as such term is defined in Rule 17Ad-15 promulgated under the Exchange Act, subject to any standards and procedures adopted by the subscription agent. See “— Medallion Guarantee May be Required.”

Medallion Guarantee May Be Required

Your signature on each subscription rights certificate must be guaranteed by an eligible institution, such as a member firm of a registered national securities exchange or a member of the Financial Industry Regulatory Authority, Inc., or a commercial bank or trust company having an office or correspondent in the United States, subject to standards and procedures adopted by the subscription agent, unless:

Subscription Agent

The subscription agent for the rights offering is American Stock Transfer & Trust Company, LLC. To exercise your subscription rights for the units, you must follow the process described in the subscription documents sent to you and also available from the information agent. You should direct any questions or requests for assistance concerning the method of subscribing for the units, or for additional copies of this prospectus and subscription documents to the information agent, D.F. King & Co., Inc., toll free at 1-800-207-2872, or by email at infoagent@dfking.com. To exercise your subscription rights for the units you will need to use the traditional paper documentation.

We will pay all fees and expenses of each of the subscription agent and the information agent related to the rights offering and have also agreed to indemnify each of the subscription agent and the information agent from certain liabilities that it may incur in connection with the rights offering.

Delivery of Subscription Materials and Payment

You should deliver your subscription rights certificate and payment of the subscription price in cash or, if applicable, notice of guaranteed delivery, to the subscription agent at the following address:

American Stock Transfer & Trust Company, LLC
6201 15th Avenue
Brooklyn, New York 11219
Attn: Corporate Actions
Tel: (718) 921.8200

Your delivery to an address or by any method other than as set forth above will not constitute valid delivery and we may not honor the exercise of your subscription rights.

You should direct any questions or requests for assistance concerning the method of subscribing for the shares of common stock or for additional copies of this prospectus to D.F. King & Co., Inc., the information agent for the rights offering, toll free at 1-800-207-2872, or by email at infoagent@dfking.com.

Guaranteed Delivery Procedures

The subscription agent will grant you three business days after the expiration date to deliver the rights certificate if you follow the following instructions for providing the subscription agent notice of guaranteed delivery. On or prior to the expiration date, the subscription agent must receive payment in full, as provided herein, for the entire amount of common stock subscribed for through the exercise of the subscription privilege, together with a properly completed and duly executed notice of guaranteed delivery substantially in the form accompanying this prospectus either by mail or overnight carrier, that specifies the name of the holder of the rights and the amount of the common stock subscribed for. If applicable, it must state separately the amount of the common stock subscribed for through the exercise of the subscription privilege and a member firm of a registered national securities exchange, a member of the Financial Industry Regulatory Authority, Inc., or a commercial bank or trust company having an office or correspondent in the United States must guarantee that the properly completed and executed rights certificate for the entire amount of the common stock subscribed for will be delivered to the subscription agent within three business days after the expiration date. The subscription agent will then conditionally accept the exercise of the rights and will withhold the common stock until it receives the properly completed and duly executed rights certificate within that time period.

Notices of guaranteed delivery and payments should be mailed or delivered to the appropriate addresses set forth under “— Delivery of Subscription Materials and Payment.”

Calculation of Subscription Rights Exercised

If you do not indicate the number of subscription rights being exercised, or do not forward full payment, as provided herein, of the total subscription price payment for the number of subscription rights that you indicate are being exercised, then you will be deemed to have exercised your subscription right with respect to the maximum

number of subscription rights that may be exercised with the aggregate subscription price payment, as provided herein, that you delivered to the subscription agent. If we do not apply your full subscription price payment to your purchase of the common stock, we or the subscription agent will return in cash the excess amount to you by mail, without interest or penalty, as soon as practicable after the expiration date of the rights offering.

To the extent you properly exercise your over-subscription privilege for an amount of shares that, following determination of the subscription price, exceeds the number of unsubscribed shares available to you, any excess subscription payments will be returned to you as soon as practicable after the expiration of the rights offering, without interest or penalty.

Escrow Arrangements

The subscription agent will hold funds received in payment of the subscription price in a segregated account until the rights offering is either completed or terminated. Funds held in escrow will only be released to the Company if the rights offering is completed. If the rights offering is terminated, all subscription funds held in escrow will be returned, without interest or penalty, to those persons who exercised their subscription rights.

Notice to Beneficial Holders

If you are a broker, a trustee or a depositary for securities that holds shares of our common stock for the account of others as of the record date, you should notify the respective beneficial owners of such shares of the rights offering as soon as possible to find out their intentions with respect to exercising their subscription rights. You should obtain instructions from the beneficial owners with respect to their subscription rights, as set forth in the instructions we have provided to you for your distribution to beneficial owners. If a beneficial owner so instructs, you should complete the appropriate subscription rights certificates and submit them to the subscription agent with the proper payment. If you did not receive this form, you should contact the subscription agent to request a copy.

Beneficial Owners

If you are a beneficial owner of shares of our common stock or will receive subscription rights through a broker, custodian bank or other nominee, we will ask your broker, custodian bank or other nominee to notify you of the rights offering. If you wish to exercise your subscription rights, you will need to have your broker, custodian bank or other nominee act for you. If you hold certificates of our common stock directly and would prefer to have your broker, custodian bank or other nominee act for you, you should contact your nominee and request it to effect the transactions for you. To indicate your decision with respect to your subscription rights, you should complete and return to your broker, custodian bank or other nominee the form entitled “Beneficial Owners Election Form”. You should receive the “Beneficial Owners Election Form” from your broker, custodian bank or other nominee with the other rights offering materials. If you wish to obtain a separate subscription rights certificate, you should contact the nominee as soon as possible and request that a separate subscription rights certificate be issued to you. You should contact your broker, custodian bank or other nominee if you do not receive this form but you believe you are entitled to participate in the rights offering. We are not responsible if you do not receive this form from your broker, custodian bank or nominee or if you receive it without sufficient time to respond.

Determinations Regarding the Exercise of Your Subscription Rights

We will decide all questions concerning the timeliness, validity, form and eligibility of the exercise of your subscription rights and any such determinations by us will be final and binding. We, in our sole discretion, may waive, in any particular instance, any defect or irregularity, or permit, in any particular instance, a defect or irregularity to be corrected within such time as we may determine. We will not be required to make uniform determinations in all cases. We may reject the exercise of any of your subscription rights because of any defect or irregularity. We will not accept any exercise of subscription rights until all irregularities have been waived by us or cured by you within such time as we decide, in our sole discretion. Our interpretations of the terms and conditions of the rights offering will be final and binding.

Neither we, nor the subscription agent, will be under any duty to notify you of any defect or irregularity in connection with your submission of subscription rights certificates and we will not be liable for failure to notify you of any defect or irregularity. We reserve the right to reject your exercise of subscription rights if your exercise is not in accordance with the terms of the rights offering or in proper form. We will also not accept the exercise of your subscription rights if our issuance of the common stock to you could be deemed unlawful under applicable law.

No Revocation or Change

Once you submit the form of rights certificate to exercise any subscription rights, you may not revoke or change your exercise or request a refund of monies paid. All exercises of rights are irrevocable, even if you subsequently learn information about us that you consider to be unfavorable, and regardless of subscription price. You should not exercise your subscription rights unless you are certain that you wish to purchase additional shares of our common stock at a subscription price that will not be determined or fixed until expiration of the rights offering period on November 8, 2016. The subscription price will be the lesser of $1.50 per share or 85% of the volume weighted average price of our common stock during market hours on the expiration date as reported on the OTC Pink Sheets.

Non-Transferability of the Rights

The subscription rights granted to you are non-transferable and, therefore, may not be assigned, gifted, purchased, sold or otherwise transferred to anyone else. Notwithstanding the foregoing, you may transfer your rights to any affiliate of yours (i.e. entities which you control or are controlled by you or under common control with you) and your rights also may be transferred by operation of law; for example, a transfer of rights to the estate of the recipient upon the death of the recipient would be permitted. If the rights are transferred as permitted, evidence satisfactory to us that the transfer was proper must be received by us prior to the expiration date.

Rights of Subscribers

You will have no rights as a holder of the common stock unless and until the common stock is delivered to you. You will have no right to revoke your subscriptions after you deliver your completed rights certificate, payment as provided herein, and any other required documents to the subscription agent.

Foreign Stockholders and Stockholders with Army Post Office or Fleet Post Office Addresses

The subscription agent will not mail rights certificates to you if you are a stockholder whose address is outside the United States or if you have an Army Post Office or a Fleet Post Office address. Instead, we will have the subscription agent hold the subscription rights certificates for your account. To exercise your rights, you must notify the subscription agent prior to 11:00 a.m., New York City time, at least three business days prior to the expiration date, and establish to the satisfaction of the subscription agent that it is permitted to exercise your subscription rights under applicable law. If you do not follow these procedures by such time, your rights will expire and will have no value.

No Board Recommendation

An investment in our common stock must be made according to your evaluation of your own best interests and after considering all of the information herein, including the “Risk Factors” section of this prospectus. Neither we nor our Board of Directors are making any recommendation regarding whether you should exercise your subscription rights.

Shares of Common Stock Outstanding After the Rights Offering

The number of shares of common stock outstanding after the rights offering will depend on the subscription price once it is established. For example, based on 54,284,296 shares of common stock outstanding as of October 12, 2016, assuming no other transactions by us involving our common stock prior to the expiration of the rights offering, and if the rights offering is fully subscribed and the subscription price is determined to be $1.50 per share (which is the maximum possible price per share in the rights offering), we will issue approximately 23,523,195 shares and have approximately 77,807,491 shares of common stock issued and outstanding (in each case, not including any shares that may be issued in payment of the fee under the backstop agreement). However, by way of further illustration, based on the same number of shares outstanding, assuming no other transactions by us involving our common stock before the expiration date and assuming the rights offering is fully subscribed at $1.36 per share (which would equate to 85% of a presumed volume weighted average price during market hours of $1.60 per share on the expiration date) we will issue approximately 25,944,700 shares and have 80,228,996 shares of common stock issued and outstanding (in each case, not including any shares that may be issued in payment of the fee under the backstop agreement).

Fees and Expenses

Neither we nor the subscription agent will charge a brokerage commission or a fee to subscription rights holders for exercising their rights. However, if you exercise your subscription rights through a broker, dealer or nominee, you will be responsible for any fees charged by your broker, dealer or nominee.

Questions About Exercising Subscription Rights

If you have any questions or require assistance regarding the method of exercising your subscription rights or requests for additional copies of this document or any document mentioned herein, you should contact the subscription agent at the address and telephone number set forth above under “— Delivery of Subscription Materials and Payment.”

Other Matters

We are not making the rights offering in any state or other jurisdiction in which it is unlawful to do so, nor are we distributing or accepting any offers to purchase any principal amount of the common stock from subscription rights holders who are residents of those states or of other jurisdictions or who are otherwise prohibited by federal or state laws or regulations to accept or exercise the subscription rights. We may delay the commencement of the rights offering in those states or other jurisdictions, or change the terms of the rights offering, in whole or in part, in order to comply with the securities law or other legal requirements of those states or other jurisdictions. Subject to state securities laws and regulations, we also have the discretion to delay allocation and distribution of any principal amount of the common stock you may elect to purchase by exercise of your subscription rights in order to comply with state securities laws. We may decline to make modifications to the terms of the rights offering requested by those states or other jurisdictions, in which case, if you are a resident in one of those states or jurisdictions or if you are otherwise prohibited by federal or state laws or regulations from accepting or exercising the subscription rights you will not be eligible to participate in the rights offering.

DESCRIPTION OF COMMON STOCK

Our Amended and Restated Certificate of Incorporation authorizes 600,000,000 shares of common stock, par value $0.0001 per share, and 20,000,000 shares of preferred stock, par value $0.0001 per share. Each holder of common stock is entitled to one vote for each share held of record on all matters submitted to a vote of the stockholders. The holders of common stock are not entitled to cumulative voting rights with respect to the election of directors, and, as a consequence, minority stockholders will not be able to elect directors on the basis of their votes alone. Holders of common stock and preferred stock are entitled to receive such dividends as may be declared by our Board of Directors out of funds legally available therefore.

In the event of a liquidation, dissolution or winding up of the company, holders of our common stock would be entitled to share ratably in all assets remaining after payment of liabilities and the satisfaction of any liquidation preference of any then outstanding series of preferred stock. Holders of common stock have no preemptive rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to the common stock. All outstanding shares of common stock are fully paid and nonassessable.

Notwithstanding the foregoing, any and all common stock and preferred stock, whether issued or outstanding prior or subsequent to the Effective Date of the Plan shall be subject to all of the terms and provisions of the Plan, including, without limitation, the cancellation of any outstanding shares of common stock and preferred stock to the extent provided in the Plan.

The Company shall not issue any non-voting equity securities in contravention of Section 1123(a)(6) of the Bankruptcy Code.

As of the record date, there were 54,284,296 shares of common stock outstanding held of record by approximately 29 stockholders.

PLAN OF DISTRIBUTION

On or about October 21, 2016, we will distribute the rights, rights certificates and copies of this prospectus to individuals who owned shares of common stock on the record date. We have not employed any brokers, dealers or underwriters in connection with the solicitation or exercise of rights in the rights offering and no commissions, fees or discounts will be paid in connection with the rights offering. While certain of our directors, officers and other employees may solicit responses from you, those directors, officers and other employees will not receive any commissions or compensation for their services other than their normal compensation. If you wish to exercise your subscription rights, you should follow the instructions in the subscription documents sent to you and also available from the information agent. If you are unable to do so, you may call the information agent for assistance. See “The Rights Offering—Method of Exercising Subscription Rights.” If you have any questions, you should contact the information agent, D.F. King & Co., Inc., toll free at 1-800-207-2872, or by email at infoagent@dfking.com. Completed subscription documentation should be completed and returned with payment for the securities as provided herein to the subscription agent, American Stock Transfer & Trust Company, LLC, at the following address:

American Stock Transfer & Trust Company, LLC
6201 15th Avenue
Brooklyn, New York 11219
Attn: Corporate Actions
Tel: (718) 921.8200

We have not entered into any agreements regarding stabilization activities with respect to our securities.

We have agreed to pay each of the subscription agent and the information agent a fee plus certain expenses, which we estimate will total approximately $20,000 and $10,000, respectively. We estimate that our total expenses in connection with the rights offering will be approximately $500,000.

Other than as described herein, we do not know of any existing agreements between any stockholder, broker, dealer, underwriter or agent relating to the sale or distribution of the shares of common stock.

BUSINESS

Overview

We are a company specializing in the development and commercialization of solutions for serious unmet medical needs and biothreats. Our lead product is TPOXX^®, also known as Tecovirimat or ST-246®, an orally administered antiviral drug that targets orthopoxvirus infections. While TPOXX^® is not yet approved as safe or effective by the FDA, it is a novel small-molecule drug that is being developed with support from BARDA and delivered to the Strategic Stockpile under Project BioShield.

BARDA Contract – TPOXX^®, also known as Tecovirimat or ST-246®

On May 13, 2011, the Company signed the BARDA Contract pursuant to which we agreed to deliver two million courses of TPOXX^® to the Strategic Stockpile. The BARDA Contract is worth approximately $472 million, including $409.8 million for manufacture and delivery of 1.7 million courses of TPOXX^® and $62 million of potential reimbursements related to development and supportive activities (the “Base Contract”). Under the Base Contract, BARDA has agreed to buy from the Company 1.7 million courses of TPOXX^®. Additionally, the Company expects to contribute to BARDA 300,000 courses of TPOXX^® at no additional cost to BARDA.

On June 28, 2016, the Company entered into a modification of the BARDA Contract (the “BARDA Contract Modification”). The total value of the BARDA Contract is unchanged. Pursuant to the BARDA Contract Modification:

In addition to the Base Contract, the BARDA Contract also contains various options that, if exercisable at BARDA: would result in a $50 million payment to the Company in the event of FDA approval for extension to 84-month expiry for TPOXX^® (from 38 month expiry as required in the Base Contract); would fund up to $58.3 million of development and supportive activities such as work on a smallpox prophylaxis indication for TPOXX^®; and/or would fund $14.4 million of production-related activities related to warm-base manufacturing. In 2015, BARDA exercised two options related to extending the indication of the drug to the geriatric and pediatric populations. The stated value of these exercises was minimal. BARDA may not exercise additional options in the future. Options are exercisable by BARDA at its sole discretion. BARDA has indicated that it will evaluate, after the FDA’s review and evaluation of stability data, the Company’s request that BARDA exercise the option for the $50 million payment to the Company in the event of FDA approval of 84-month expiry for TPOXX^®.

The BARDA Contract expires in September 2020.

For courses of TPOXX^® that are physically delivered to the Strategic Stockpile, the Company has replacement obligations, at no cost to BARDA, in the event that the final version of TPOXX^® approved by the FDA is different from any course of TPOXX^® that has been delivered to the Strategic Stockpile or if TPOXX^® does not meet any specific label claims, fails release testing or does not meet 38 month expiry period (from time of delivery to the Strategic Stockpile), or if TPOXX^® is recalled or deemed to be recalled for any reason.

The Company is eligible for a $41.0 million hold back payment from BARDA if the FDA approves TPOXX^®, either in the currently delivered form or in a different form. The hold back payment is part of the $409.8 million of

payments that can be received by the Company for the manufacture and delivery of 1.7 million courses of TPOXX