Altimmune stock falls after MASH treatment trial results

Altimmune, Inc. (NASDAQ:ALT) shares plummeted 37% after the company reported topline results from its IMPACT Phase 2b trial for pemvidutide in MASH. While the drug met its primary endpoint for MASH resolution in up to 59.1% of participants and demonstrated significant weight loss and favorable tolerability, investor concern appears to stem from the lack of statistical significance in fibrosis improvement in the primary analysis. Despite this, Altimmune highlighted a supplemental AI-based analysis showing statistically significant fibrosis reduction and expressed confidence in advancing pemvidutide to Phase 3 trials following an End of Phase 2 meeting with the FDA in Q4 2025.

Analysis

Altimmune, Inc. (ALT) experienced a severe 37% stock price decline despite its Phase 2b IMPACT trial for pemvidutide meeting its primary endpoint for metabolic dysfunction-associated steatohepatitis (MASH). The market's strongly negative reaction indicates that investors are prioritizing the trial's failure to demonstrate a statistically significant improvement in fibrosis over the successful primary endpoint of MASH resolution, which was achieved in up to 59.1% of participants. While the drug showed significant weight loss (up to 6.2%) and favorable tolerability, the fibrosis improvement rates of 31.8% and 34.5% in the treatment arms were not statistically superior to the 25.9% rate in the placebo group. The company is attempting to mitigate this outcome by highlighting a supplemental AI-based analysis that did show statistically significant fibrosis reduction and by stating its intention to proceed with an End of Phase 2 meeting with the FDA, though this is not scheduled until the fourth quarter of 2025. The market is clearly discounting the positive primary endpoint and the supplemental AI data, focusing instead on the key secondary endpoint failure, which is a critical measure for a MASH therapeutic's competitive profile and regulatory prospects.

Key Decisions for Investors

• Investors should recognize that the lack of statistically significant fibrosis improvement is a major clinical overhang, and the market's reaction suggests deep skepticism about the drug's competitive viability against other MASH treatments where this endpoint is met.
• The next key catalyst is regulatory feedback from the FDA, so investors should monitor for any updates on whether the agency will accept the supplemental AI-based analysis as sufficient for a path to Phase 3 trials.
• Given the planned End of Phase 2 meeting is not until Q4 2025, investors must be prepared for a prolonged period of uncertainty and potential share price volatility, making this a high-risk holding suitable only for those with a long-term investment horizon and high tolerance for clinical trial risk.