Overview

A class action lawsuit has been filed against Altimmune, Inc. (“Altimmune” or the “Company”) and certain of the Company’s former senior executive officers alleging violations of the federal securities laws. The Company’s common stock traded on the Nasdaq Stock Exchange (the “NASDAQ”) under the symbol “ALT.”

The Altimmune class action lawsuit was brought on behalf of all persons and entities who purchased or otherwise acquired Altimmune securities between August 10, 2023, and June 25, 2025, both dates inclusive, (the “Class Period”).

Altimmune is a clinical stage biopharmaceutical company focused on developing treatments for obesity, metabolic and liver diseases. The Company’s lead product candidate, pemvidutide (formerly known as ALT-801), is a novel, investigational, peptide-based GLP[1]1/glucagon dual receptor agonist. Pemvidutide is currently in clinical development for obesity and metabolic associated steatohepatitis (“MASH”).

The Altimmune lawsuit centers on allegations that the Company and its executives misled investors about the results of its IMPACT Phase 2b MASH trial for pemvidutide, particularly regarding the fibrosis reduction primary endpoint. Leading up to the release of topline results, Defendants allegedly issued overwhelmingly positive statements that failed to account for the higher-than-expected fibrosis reduction observed in the placebo group.

According to the lawsuit, Altimmune repeatedly promoted optimistic expectations for the trial, even issuing a press release titled “Announces Positive Topline Results from the IMPACT Phase 2b MASH trial of Pemvidutide in the Treatment of MASH,” despite the fact that one of the two primary endpoints—fibrosis reduction—did not achieve statistical significance. The lawsuit further alleges that during the Special Call to discuss the results, executives spent minimal time addressing this shortcoming and instead downplayed it by expressing hope for better outcomes in the upcoming Phase 3 trial.

On June 26, 2025, Altimmune released the topline Phase 2b results, revealing that statistical significance for fibrosis reduction was not met, with executives attributing the failure to the trial’s Phase 2 status and a stronger-than-expected placebo response. The market reacted sharply to the disclosure, sending Altimmune’s share price tumbling from $7.71 on June 25, 2025, to $3.61 on June 26, 2025—a 53.2% drop in a single trading day. The lawsuit claims that investors who purchased shares before the disclosure did so based on materially misleading information and suffered substantial losses as a result.

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If you purchased or otherwise acquired Altimmune securities between August 10, 2023, and June 25, 2025, both dates inclusive, and you wish to serve as lead plaintiff in this lawsuit, we encourage you to submit your information to DiCello Levitt LLP via the form on this page. 

You can also contact DiCello Levitt partner Brian O’Mara by calling (888) 287-9005 or at investors@dicellolevitt.com. 

The deadline to apply to the Court to serve as lead plaintiff in the Altimmune class action lawsuit is October 6, 2025.