Altimmune, Inc.

On June 4, 2024, a shareholder derivative complaint was filed in federal district court in the District of Delaware, purportedly on behalf of us, naming as defendants three of our executive officers and eight of our board members, which is now captionedIn re Altimmune, Inc. Stockholder Derivative Litigation, No. 1:24-cv-669 (D. Del.) (the “Derivative Action”). The complaint is based upon allegations that are similar to those alleged in a class action complaint previously filed against usIn re Altimmune, Inc. Securities Litigation, No. 24-cv-01315 (D. Md.) (the “Class Action”) and alleges claims for contribution, breaches of fiduciary duty, unjust enrichment, and waste of corporate assets based on the defendants purportedly making or causing to be made false and misleading statements and omissions of material fact between December 1, 2023 and April 26, 2024. The complaint seeks unspecified monetary relief, exemplary damages, restitution, contribution, and costs, as well as equitable relief. A similar shareholder derivative complaint, captioned Alaraidah v. Garg, et al., No. 1:24-cv-00772 (D. Del.), was filed in the same court by another plaintiff on July 1, 2024, based upon substantially similar allegations, and alleges claims for contribution, breach of fiduciary duties, unjust enrichment, abuse of control, gross mismanagement, and waste of corporate assets and seeks unspecified monetary relief, restitution, costs, and equitable relief. These actions were consolidated for all purposes on July 18, 2024 into the Derivative Action. On February 3, 2025, pursuant to a joint stipulation of the parties, the court ordered that the Derivative Action be dismissed without prejudice and the case was closed.

On August 5, 2025, a class action complaint was filed in federal district court in the District of Maryland, Southern Division, naming as defendants the Company and two of the Company’s executive officers, captionedCollier v. Altimmune, Inc., et al., Case No. 8:25-cv-02581 (D. Md.) (the “Collier Class Action”). The Collier Class Action alleges that the defendants violated Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended, and Rule 10b-5 thereunder, by making false and misleading statements and omissions of material fact to the investing public including the plaintiff and class members, who purchased or otherwise acquired the Company’s common stock between August 10, 2023 and June 25, 2025, including relating to pemvidutide and our IMPACT Phase 2b trial of pemvidutide in MASH. The plaintiff and class members seek, among other things, to have the action maintained as a class action under Rule 23 of the Federal Rules of Civil Procedure and for the defendants to pay damages, interest, and an award of costs, including attorneys’ fees. We intend to defend vigorously against this litigation.

From time to time, we may be involved in various legal proceedings or investigations, which could be costly and impose a significant burden on management and employees. The results of any current or future litigation cannot be predicted with certainty, and regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs, diversion of management resources, and other factors.