Altimmune shares plunge as MASH drug trial misses key fibrosis endpoint

Altimmune Inc. shares plummeted 55% following mixed Phase 2b trial results for its MASH drug, pemvidutide. While the drug met its primary endpoint of MASH resolution without worsening of fibrosis, it notably failed to achieve statistically significant improvement in liver fibrosis, a more challenging and critical measure, compared to placebo. Despite this key miss, Altimmune plans to advance to a Phase 3 program after an FDA meeting, though the fibrosis data significantly impacted investor confidence.

Analysis

Altimmune Inc. (NASDAQ:ALT) experienced a 55% collapse in its share price following the release of mixed results from its Phase 2b trial for pemvidutide, a treatment for metabolic dysfunction-associated steatohepatitis (MASH). The study successfully met one of its primary endpoints, demonstrating statistically significant MASH resolution without worsening of fibrosis in 59.1% and 52.1% of patients at different dosages, compared to just 19.1% for placebo. However, the trial critically failed to meet its other primary endpoint: a statistically significant improvement in liver fibrosis. Fibrosis improvement was observed in only 31.8% and 34.5% of patients in the treatment arms versus 25.9% in the placebo group, a difference that was not statistically significant. This failure on the more challenging fibrosis endpoint represents a significant clinical setback. Despite this, Altimmune management intends to proceed to a Phase 3 program following a Q4 2025 meeting with the FDA and will analyze 48-week data to assess if longer treatment duration yields better fibrosis outcomes. While Jefferies analysts suggest the overall data supports continued development, the lack of a clear anti-fibrotic effect significantly dampens the drug's competitive profile and has severely impacted investor confidence.

Key Decisions for Investors

• Investors should recognize that the failure to meet the liver fibrosis endpoint significantly elevates the risk profile of pemvidutide and introduces substantial uncertainty regarding its future regulatory approval and commercial potential in the competitive MASH market.
• The upcoming End-of-Phase 2 meeting with the FDA in Q4 2025 is now a critical catalyst; the agency's feedback on the viability of a Phase 3 program based on this mixed data will be a key determinant of the company's future.
• Given the 55% share price decline, a re-evaluation of Altimmune's valuation is warranted, weighing the successful MASH resolution data against the heightened risk from the pivotal fibrosis miss.
• Monitor for the 48-week follow-up data, as any statistically significant improvement in fibrosis with longer treatment could partially de-risk the asset and offer a potential, albeit delayed, recovery path.