Material Agreement (Form 8-K)

Item 1.01. Entry into a Material Definitive Agreement.

On January 27, 2026, Altimmune, Inc. (the "Company") entered into a Securities Purchase Agreement with a new fundamental institutional investor (the "Securities Purchase Agreement") relating to the issuance of 12,397,920 shares of the Company's common stock, par value of $0.0001 per share (the "Common Stock") and pre-funded warrants (the "Pre-Funded Warrants") to purchase up to 4,647,534 shares of Common Stock (such shares of Common Stock issuable upon exercise of the Pre-Funded Warrants, the "Pre-Funded Warrant Shares") to such investor in a registered direct offering (the "Offering"). The closing of the Offering is expected to take place on or about January 29, 2026, subject to the satisfaction of customary closing conditions.

The Company also entered into a Placement Agency Agreement with Titan Partners Group LLC, a division of American Capital Partners, LLC ("Titan Partners") (the "Placement Agency Agreement," and together with the Securities Purchase Agreement, the "Agreements"), who is acting as the sole placement agent for the Offering.

The Agreements contain customary representations, warranties and covenants of the Company and also provide for customary indemnification obligations of the Company, including the liabilities under the Securities Act of 1933, as amended. In connection with the Offering, the Company, and each of the Company's directors and executive officers have entered into "lock-up" agreements that generally prohibit, without the prior written consent of Titan Partners, the sale, transfer or dispositions of securities of the Company for a period of 30 days following the closing of the Offering, subject to customary exceptions.

The gross proceeds from the Offering will be approximately $75 million, before paying the placement agent fees and other estimated offering expenses. The Offering is being made pursuant to the shelf registration statement on Form S-3 (File No. 333-291329) previously filed by the Company with the Securities and Exchange Commission (the "SEC") on November 6, 2025 and declared effective on December 5, 2025. The Offering is made only by means of a prospectus forming a part of the effective registration statement and a prospectus supplement relating to the Offering.

Each Pre-Funded Warrant is exercisable for one share of common stock. The purchase price of each Pre-Funded Warrant will equal the price per share at which shares of the Company's common stock are being sold to the public in this offering, less the $0.001 exercise price of each Pre-Funded Warrant. The Pre-Funded Warrants do not expire, and each Pre-Funded Warrant will be exercisable at any time after the date of issuance, subject to an ownership limitation. The "Beneficial Ownership Limitation" shall be 9.99% of the number of shares of the Common Stock outstanding immediately after giving effect to the issuance of shares of Common Stock issuable upon exercise of the Pre-Funded Warrant. The Holder, upon written notice to the Company, may increase or decrease the Beneficial Ownership Limitation provisions, provided that the Beneficial Ownership Limitation in no event exceeds 19.99% of the number of shares of the Common Stock outstanding immediately after giving effect to the issuance of shares of Common Stock upon exercise of the Pre-Funded Warrant, with additional provisions continuing to apply. Any increase in the Beneficial Ownership Limitation will not be effective until the 61st day after such notice is delivered to the Company. The Company does not intend to list the Pre-Funded Warrants on the Nasdaq Global Market, any other national securities exchange or any other nationally recognized trading system. The foregoing summary of the Pre-Funded Warrant is qualified in its entirety by reference to the form of Pre-Funded Warrant, a copy of which is attached hereto as Exhibit 4.1 and incorporated herein by reference.

In connection with the Placement Agency Agreement, the Company agreed to pay Titan Partners a cash fee based on the gross proceeds raised from the sale and issuance of the shares of Common Stock and Pre-Funded Warrants. Pursuant to the Placement Agency Agreement, the Company also agreed to reimburse Titan Partners up to $125,000 for its expenses.

The form of Pre-Funded Warrant, Securities Purchase Agreement and Placement Agency Agreement are filed as Exhibit 4.1, 10.1 and 10.2, respectively, to this Current Report on Form 8-K. The foregoing description of the respective terms of the Agreements and Pre-Funded Warrant is not intended to be complete and is qualified in its entirety by reference to each such exhibit. A copy of the opinion of Goodwin Procter LLP relating to the legality of the issuance and sale of the securities in the Offering is filed as Exhibit 5.1 to this Current Report on Form 8-K.

This Current Report on Form 8-K shall not constitute an offer to sell or the solicitation of an offer to buy the securities discussed herein, nor shall there be any offer, solicitation, or sale of the securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.

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