UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ☒ Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the fiscal year ended December 31, 2019 ☐ Transition Report under Section 13 or 15(d) of the Securities Exchange Act of 1934 For the transition period from to Commission File Number: 001-32587 ALTIMMUNE, INC. (Exact name of registrant as specified in its charter) Delaware 20-2726770 (State or other jurisdiction of (I.R.S. Employer incorporation or organization) Identification No.) 910 Clopper Road, Suite 201S, Gaithersburg, MD 20878 (Address of principal executive offices) (Zip Code) Registrant’s telephone number, including area code (240) 654-1450 Securities registered pursuant to Section 12(b) of the Act: Title of each class Trading Symbol(s) Name of each exchange on which registered Common stock, par value $0.0001 per share ALT The NASDAQ Global Market Securities registered pursuant to Section 12(g) of the Act: None Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐ No ☒ Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ☐ No ☒ Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐ Indicate by check mark whether the registrant has submitted electronically every Interactive Data file required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐ Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act. Large accelerated filer ☐ Accelerated filer ☐ Non-accelerated filer ☒ Smaller reporting company ☒ Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐ Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes ☐ No ☒ The aggregate market value of the Registrant’s common stock held by non-affiliates, based upon the closing price of the Registrant’s common stock on the NASDAQ Global Market of $2.38, on June 28, 2019 was approximately $28,792,136. There were 15,361,660 shares of the Registrant’s common stock, $0.0001 par value per share, outstanding on March 26, 2020. ALTIMMUNE, INC. ANNUAL REPORT ON FORM 10-K TABLE OF CONTENTS Page PART I Item 1. Business ............................................................................................................................................................................. 2 Item 1A. Risk Factors ........................................................................................................................................................................ 25 Item 1B. Unresolved Staff Comments .............................................................................................................................................. 64 Item 2. Properties ........................................................................................................................................................................... 64 Item 3. Legal Proceedings .............................................................................................................................................................. 64 Item 4. Mine Safety Disclosures ..................................................................................................................................................... 64 PART II Item 5. Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities ......... 65 Item 6. Selected Financial Data ...................................................................................................................................................... 65 Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations ............................................. 66 Item 7A. Quantitative and Qualitative Disclosures about Market Risk ............................................................................................. 77 Item 8. Financial Statements and Supplementary Data .................................................................................................................. 78 Item 9. Changes in and Disagreements with Accountants on Accounting and Financial Disclosure ............................................. 108 Item 9A. Controls and Procedures ..................................................................................................................................................... 108 Item 9B. Other Information ............................................................................................................................................................... 108 PART III Item 10. Directors, Executive Officers and Corporate Governance ................................................................................................. 109 Item 11. Executive Compensation .................................................................................................................................................... 115 Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters ........................... 121 Item 13. Certain Relationships and Related Transactions, and Director Independence ................................................................... 122 Item 14. Principal Accountant Fees and Services............................................................................................................................. 123 PART IV Item 15. Exhibits and Financial Statement Schedules ...................................................................................................................... 125 Item 16. Form 10-K Summary ......................................................................................................................................................... 127 Signatures ........................................................................................................................................................................... 128 [This page intentionally left blank] PART I Forward-looking statements This Annual Report on Form 10-K for the year ended December 31, 2019 (this “Annual Report”) contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the Private Securities Litigation Reform Act of 1995. Written or oral statements that constitute forward-looking statements may be made by us or on our behalf. Words such as “expect,” “anticipate,” “intend,” “plan,” “believe,” “estimate,” “may,” “will,” “should,” “could,” “target,” “strategy,” “intend,” “project,” “guidance,” “likely,” “usually,” “potential,” or the negative of these words or variations of such words, similar expressions, or comparable terminology are intended to identify such forward-looking statements, although not all forward-looking statements contain these identifying words. There are a number of important risks and uncertainties that could cause our actual results to differ materially from those indicated by forward-looking statements. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward- looking statements we make. These forward-looking statements are based on current expectations, estimates, forecasts, and projections about the industry and markets in which we operate, and management’s beliefs and assumptions. These statements are not guarantees of future performance and involve certain risks, uncertainties, and assumptions that are difficult to predict and may cause our actual results, performance or achievements to be materially different from future results, performance or achievements expressed or implied by any forward-looking statements. These risks, uncertainties and other factors include, but are not limited to, risks associated with the following: • our ability to develop and commercialize our current and future product candidates; • our ability to expand our pipeline of product candidates and the success of future product candidate advancements, including the success of future clinical trials, and our ability to commercialize our products; • the reliability of the results of the studies relating to human safety and possible adverse effects