Altimmune, Inc.

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, which was captionedIn re Altimmune, Inc. Securities Litigation, Case No. 8:25-cv-02581 (D. Md.) (the “Securities Class Action”). The Securities Class Action alleged 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 sought, 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. On October 16, 2025, the court appointed lead plaintiffs for the litigation. On October 29, 2025, the court entered an order requiring lead plaintiffs to file an amended complaint by November 26, 2025, and for defendants to file an answer or notice of intent to file a motion to dismiss such amended complaint by December 10, 2025. Rather than amend, the lead plaintiffs sought voluntary dismissal without prejudice of the action, which the Court granted on November 26, 2025.

On September 29, 2025, a shareholder derivative complaint was filed in federal district court in the District of Maryland, purportedly on behalf of the Company, naming as defendants two of the Company’s then-executive officers and eight of the Company’s current and former board members, captionedAlaraidah v. Altimmune, Inc., et al., No. 8:25-cv-03223 (D. Md.) (the “Derivative Action”). The complaint was based upon allegations that were similar to those alleged in a class action complaint previously filed against us in the Securities Class Action and alleged claims for violations of Section 14(a) of the Securities Exchange Act of 1934, breaches of fiduciary duty, unjust enrichment, abuse of control, gross mismanagement, waste of corporate assets, and contribution under Sections 10(b) and 21D of the Securities Exchange Act of 1934 based on the defendants purportedly making or causing to be made false and misleading statements and omissions of material fact between August 10, 2023 and June 25, 2025. The complaint sought unspecified monetary relief, restitution, costs, and equitable relief. On December 22, 2025, the parties filed a stipulation of dismissal without prejudice, which the Court granted on that date.

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.