STOCK PURCHASE AGREEMENT

Exhibit 10.10

STOCK PURCHASE AGREEMENT

     This Stock Purchase Agreement (this “ Agreement ”) is dated June 30, 2009, by and between Laboratorios Farmaceuticos ROVI S.A., a public limited company organized and existing under the laws of Spain (the “ Investor ”), and Novavax, Inc., a Delaware corporation (the “ Company ” and, together with the Investor, the “ Parties ”), whereby the parties agree as set forth herein. Certain terms are defined in Section 9 of this Agreement.

      WHEREAS , the Parties have entered into an Amended and Restated Head of Terms dated as of June 30, 2009 (the “ Head of Terms ”) providing the terms and conditions pursuant to which the Parties intend to negotiate definitive agreements for a collaboration to develop and commercialize certain vaccines; and

      WHEREAS , in connection with the collaboration, the Investor has also agreed to make an equity investment in the Company, in accordance with the terms and conditions set forth in this Agreement.

      NOW, THEREFORE , in consideration of the premises and the mutual promises herein made, and in consideration of the representations, warranties, and covenants herein contained, the Parties agree as follows:

          1. Subscription .

               (a) Investor agrees to buy and the Company agrees to sell and issue to Investor 1,094,891 shares (the “ Shares ”) of the Company’s common stock, $0.01 par value per share (the “ Common Stock ”), at a per share price of $2.74 for an aggregate purchase price of $3,000,001.34 (the “ Purchase Price ”).

               (b) The Shares have been registered on a Registration Statement on Form S-3, Registration No. 333-138893 (the “ Registration Statement ”), which registration statement has been declared effective by the Securities and Exchange Commission (the “ Commission ”) and is effective on the date hereof (together with any registration statement filed by the Company pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the “ Securities Act ”)). A final prospectus supplement will be delivered to the Investor as required by law.

               (c) On the closing date, which, in accordance with Rule 15c6-1 promulgated under the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), is expected to occur on or about July 1, 2009 (the “ Closing Date ”), upon satisfaction or waiver of all the conditions to closing set forth in this Agreement, (i) the Purchase Price for the Shares purchased by the Investor will be delivered by or on behalf of the Investor to the Company against delivery of the Shares, and (ii) the Company shall cause its transfer agent to release to the Investor the number of Shares being purchased by the Investor (such release shall be made through the facilities of The Depository Trust Company’s DWAC system). The provisions set forth in Exhibit A hereto shall be incorporated herein by reference as if set forth fully herein.

          2. Representations, Warranties and Agreements of the Company . The Company represents and warrants to and agrees with Investor as of the date hereof and as of the Closing Date and any other date specified below, that:

               (a) The Company has been duly incorporated and has a valid existence and the authorization to transact business as a corporation under the laws of the State of Delaware, with corporate power and authority to own its properties and conduct its business as described in the Prospectus, and has been duly qualified as a foreign corporation for the transaction of business and is in good standing under the laws of each other jurisdiction in which it owns or leases properties or conducts any business so as to require such qualification, except for such jurisdictions wherein the failure to be so qualified and in good standing would not individually or in the aggregate have a Material Adverse Effect.

               (b) The subsidiary of the Company, Fielding Pharmaceutical Company, has been duly incorporated and is validly existing as a corporation in good standing under the laws of the State of Delaware, with corporate power and authority to own its properties and conduct its business as described in the Prospectus, and has been duly qualified as a foreign corporation for the transaction of business and is in good standing under the laws of each other jurisdiction in which it owns or leases properties or conducts any business so as to require such qualification, except for such jurisdictions wherein the failure to be so qualified and in good standing would not individually or in the aggregate have a Material Adverse Effect. All of the outstanding capital stock or other voting securities of the subsidiary is owned by the Company, directly or indirectly, free and clear of any lien and free of any other limitation or restriction (including any restriction on the right to vote, sell or otherwise dispose of such capital stock or other voting securities). Other than the Company’s 4.75% senior convertible notes (the “ Convertible Notes ”) and warrants to purchase 3,343,325 of Company Common Stock (the “ 2008 Warrants ”), there are no outstanding (i) securities of the Company or its subsidiary which are convertible into or exchangeable for shares of capital stock or voting securities of the subsidiary or (ii) options or other rights to acquire from the Company or its subsidiary, or other obligation of the Company or its subsidiary to issue, any capital stock, voting securities or securities convertible into or exchangeable for capital stock or voting securities of the subsidiary (collectively, the “ Subsidiary Securities ”). There are no outstanding obligations of the Company or its subsidiary to repurchase, redeem or otherwise acquire any outstanding Subsidiary Securities.

               (c) The execution, delivery and performance of this Agreement by the Company and the consummation of the transactions contemplated hereby are within the corporate powers of the Company and have been duly authorized by all necessary corporate action on the part of the Company, and this Agreement, when duly executed and delivered by the Company, will constitute a valid and legally binding instrument of the Company enforceable in accordance with its terms, except as enforcement hereof may be limited by the effect of any applicable bankruptcy, insolvency, reorganization or similar laws or court decisions affecting enforcement of creditors’ rights generally and except as enforcement hereof is subject to general principles of equity (regardless of whether enforcement is considered in a proceeding in equity or at law).

               (d) The Shares have been duly authorized by the Company, and when issued and delivered by the Company against payment therefor as contemplated by this Agreement, the Shares will (i) be validly issued, fully paid and nonassessable, (ii) not be subject to any statutory or contractual preemptive rights or other rights to subscribe for or purchase or acquire any shares of Common Stock, which have not been waived or complied with, and (iii) conform to the description of the Common Stock contained in the Prospectus. The capital stock of the Company, including the Common Stock, conforms as to the legal matters to the description thereof, if any, contained in the Registration Statement and the Prospectus, and as of the date thereof, the Company had authorized capital stock as set forth therein. The Shares are in due and

proper form and the holders of Shares will not be subject to personal liability by reason of being such holders.

               (e) The execution and delivery of the Agreement does not, and the compliance by the Company with the terms hereof will not, (i) violate the Certificate of Incorporation (as amended to date) of the Company or the By-Laws (as amended to date) of the Company, (ii) result in a breach or violation of any of the terms or provisions of, or constitute a default under, any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company or its subsidiary is bound, or (iii) result in a violation of, or failure to be in compliance with, any applicable statute or any order, judgment, decree, rule or regulation of any court or governmental, regulatory or self-regulatory agency or body having jurisdiction over the Company or its subsidiary, except in the case of (ii) and (iii) where such breach, violation, default or the failure to be in compliance would not have a Material Adverse Effect; and no consent, approval, authorization, order, registration, filing or qualification of or with any such court or governmental, regulatory or self-regulatory agency or body is required for the valid authorization, execution, delivery and performance by the Company of the Agreement or the issuance of the Shares, except for such consents, approvals, authorizations, registrations, filings or qualifications as may be required under the Securities Act or state securities or “blue sky” laws and have been or will be obtained and which have been or will be made in connection with the listing of the Shares on the NASDAQ Global Market.

               (f) The Company meets the requirements for the use of Form S-3 under the Securities Act for the primary issuance of securities. The Registration Statement has been declared effective by the Commission and at the time it became effective, and as of the date hereof, the Registration Statement complied and complies with Rule 415 under the Securities Act. No stop order suspending the effectiveness of the Registration Statement has been issued and no proceeding for that purpose has been initiated or, to the Company’s knowledge, threatened by the Commission. On the effective date of the Registration Statement, the Registration Statement complied, on the date of the Prospectus, the Prospectus will comply, and at the date of the Closing, the Registration Statement and the Prospectus will comply, in all material respects with the applicable provisions of the Securities Act and the applicable rules and regulations of the Commission thereunder; on the effective date of the Registration Statement, the Registration Statement did not, on the date of the Prospectus, the Prospectus did not, and at the date of the Closing, the Registration Statement and the Prospectus will not, contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in light of the circumstances under which they were made (with respect to the Prospectus), not misleading; and when filed with the Commission, the documents incorporated by reference in the Registration Statement and the Prospectus, complied or will comply in all material respects with the applicable provisions of the Exchange Act and the applicable rules and regulations of the Commission thereunder. There is no material document of a character required to be described in the Registration Statement or the Prospectus or to be filed as an exhibit to the Registration Statement that is not described or filed as required.

               (g) The consolidated financial statements of the Company included or incorporated by reference in the Registration Statement and the Prospectus comply as to form with the applicable accounting requirements of the Securities Act and have been prepared in conformity with generally accepted accounting principles (except, with respect to the unaudited consolidated financial statements and the accompanying footnotes which are subject to customary audit adjustments) applied on a consistent basis, are consistent in all material respects with the books and records of the Company, and accurately present in all material respects the consolidated financial position, results of operations and cash flow of the Company and its

subsidiary as of and for the periods covered thereby. There are no other financial statements (historical or pro forma) that are required to be included in the Registration Statement and the Prospectus.

               (h) There are no material liabilities of the Company or its subsidiary of any kind whatsoever, whether accrued, contingent, absolute, determined, determinable or otherwise, and there is no existing condition, situation or set of circumstances which could reasonably be expected to result in such a liability, other than liabilities disclosed in the consolidated financial statements and financial schedules of the Company included or incorporated by reference in the Registration Statement and the Prospectus, and other undisclosed liabilities which, individually or in the aggregate, are not material to the Company and its subsidiary, taken as a whole.

               (i) Neither the Company nor its subsidiary has sustained, since the date of the latest audited consolidated financial statements included or incorporated by reference in the Registration Statement and Prospectus, any material loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor dispute or court or governmental action, order or decree, otherwise than as disclosed in or contemplated by the Registration Statement and Prospectus; and, since the date as of which information is given in the Prospectus, there has not been any material change in the capital stock or long-term debt of the Company or its subsidiary, the Company and its subsidiary have not incurred any material liabilities or obligations, direct or contingent, nor entered into any material transactions, except for entering into purchase orders in the ordinary course of business, and there has not been any material adverse change in or affecting the general affairs, assets, business, management, financial position or condition, stockholders’ equity or results of operations of the Company and its subsidiary considered as a whole, otherwise than as disclosed in the Registration Statement and Prospectus.

               (j) Other than as disclosed or incorporated by reference in the Prospectus, there are no legal, governmental or regulatory proceedings pending to which the Company or its subsidiary is a party or of which any material property of the Company or its subsidiary is the subject which, taking into account the likelihood of the outcome, the damages or other relief sought and other relevant factors, would individually or in the aggregate reasonably be expected to have a Material Adverse Effect or adversely affect the ability of the Company to issue and sell the Shares; to the best of the Company’s knowledge, no such proceedings are threatened or contemplated by governmental or regulatory authorities or threatened by others.

               (k) The Company and its subsidiary have good and marketable title to all the real property and own all other properties and assets, reflected as owned in the financial statements included or incorporated by reference in the Registration Statement and the Prospectus, subject to no lien, mortgage, pledge, charge or encumbrance of any kind except those, if any, reflected in such financial statements or which are not material to the Company and its subsidiary taken as a whole. The Company and its subsidiary hold their respective leased real and personal properties under valid and binding leases, except where the failure to do so would not reasonably be expected to individually or in the aggregate have a Material Adverse Effect.

               (l) The Company has filed all necessary federal and state income and franchise tax returns and has paid all taxes shown as due thereon or has filed all necessary extensions, and there is no tax deficiency that has been, or to the knowledge of the Company might be, asserted against the Company or any of its properties or assets that would in the aggregate or individually reasonably be expected to have a Material Adverse Affect.

               (m) There are no authorized options, warrants, preemptive rights, rights of first refusal or other rights to purchase, or equity or debt securities convertible into or exchangeable or exercisable for, any capital stock of the Company or its subsidiary other than those described in the Registration Statement and the Prospectus or in documents incorporated by reference therein. There are no holders or beneficial owners of securities of the Company having rights to registration thereof whose securities have not been previously registered or who have not waived such rights with respect to the registration of the Company’s securities on the Registration Statement, except where the failure to obtain such waiver would not individually or in the aggregate reasonably be expected to have a Material Adverse Effect.

               (n) Other than as disclosed in the Prospectus, the Company together with its subsidiary owns and possesses all right, title and interest in and to, or, to the Company’s knowledge, has duly licensed from third parties, all patents, patent rights, trade secrets, inventions, know-how, trademarks, trade names, copyrights, service marks and other proprietary rights (“ Intellectual Property ”) material to the business of the Company and its subsidiary taken as a whole as currently conducted and as described in the Prospectus. To the Company’s knowledge and except as would not individually or in the aggregate have a Material Adverse Effect, there is no infringement or other violation by third parties of any of the Intellectual Property of the Company. Neither the Company nor its subsidiary has received any notice of infringement or misappropriation from any third party that has not been resolved or disposed of. Further, there is no pending or, to the Company’s knowledge and except as would not individually or in the aggregate have a Material Adverse Effect, threatened action, suit, proceeding or claim by governmental authorities or others that the Company is infringing a patent, and there is no pending or, to the Company’s knowledge and except as would not individually or in the aggregate have a Material Adverse Effect, threatened legal or administrative proceeding relating to patents and patent applications of the Company, other than proceedings initiated by the Company before the United States Patent and Trademark Office and the patent offices of certain foreign jurisdictions which are in the ordinary course of patent prosecution. To the Company’s knowledge, the patent applications of the Company presently on file disclose patentable subject matter, and the Company is not aware of any inventorship challenges, any interference which has been declared or provoked, or any other material fact that (i) would preclude the issuance of patents with respect to such applications, or (ii) would lead outside patent counsel for the Company to reasonably conclude that such patents, when issued, would not be valid and enforceable in accordance with applicable regulations.

               (o) The Company conducts its business in compliance in all respects with applicable laws, rules and regulations of governmental and regulatory bodies to which it is subject, except where the failure to be in compliance would not have a Material Adverse Effect.

               (p) All offers and sales of the Company’s capital stock prior to the date hereof were at all relevant times registered pursuant to the Securities Act or exempt from the registration requirements of the Securities Act and were issued in compliance in all material respects with applicable state securities or blue sky laws.

               (q) The Company has filed with the NASDAQ Global Market a Notification of Listing of Additional Shares with respect to the Shares required by the rules of the NASDAQ Global Market and has not received a notice from the NASDAQ Global Market that such notification is insufficient. The offer and sale of the Shares does not require stockholder approval under Rule 5635 of the NASDAQ Listing Rules.

               (r) Neither the Company nor its subsidiary nor, to the best of the Company’s knowledge, any employee or agent of the Company or its subsidiary, has (i) used any corporate funds for unlawful contributions, gifts, entertainment or other unlawful expenses relating to political activity, (ii) made any unlawful payment to foreign or domestic government officials or employees or to foreign or domestic political parties or campaigns from corporate funds, (iii) violated any provision of the Foreign Corrupt Practices Act of 1977, as amended, or (iv) made any other unlawful payment.

               (s) There is no broker, finder or other party that is entitled to receive from the Company any brokerage or finder’s fee or other fee or commission as a result of any transactions contemplated by this Agreement.

               (t) The Company maintains a system of internal accounting controls sufficient to provide reasonable assurances that (i) transactions are executed in accordance with management’s general or specific authorization; (ii) transactions are recorded as necessary to permit preparation of consolidated financial statements in conformity with generally accepted accounting principles and to maintain accountability for assets; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; and (iv) the recorded accountability for assets is compared with existing assets at reasonable intervals and appropriate action is taken with respect to any differences. Except as described in the Registration Statement and the Prospectus, since the most recent audit of the effectiveness of the Company’s internal control over financial reporting, there has been (i) no material weakness in the Company’s internal control over financial reporting (whether or not remediated) and (ii) no change in the Company’s internal control over financial reporting that has materially affected, or is reasonably likely to materially affect, the Company’s internal control over financial reporting.

               (u) The Company has established, maintains and evaluates “disclosure controls and procedures” (as such term is defined in Rule 13a-15(e) and 15d-15(e) under the Exchange Act), which (i) are designed to ensure that material information relating to the Company is made known to the Company’s principal executive officer and its principal financial officer by others within the Company and its subsidiary, particularly during the periods in which the periodic reports required under the Exchange Act are being prepared, (ii) have been evaluated for effectiveness as of the end of the last fiscal period covered by the Registration Statement; and (iii) such disclosure con