Altimmune, Inc. (ALT) experienced a surprising pre-market plunge of 6.49% on Thursday, despite announcing positive topline results from its IMPACT Phase 2B trial of pemvidutide in the treatment of Metabolic dysfunction-Associated SteatoHepatitis (MASH). The unexpected stock movement has left investors puzzled, given the seemingly favorable clinical outcomes.

The company reported that the trial met its primary endpoint, achieving a 59.1% MASH resolution without worsening fibrosis. Additionally, the study demonstrated weight loss of up to 6.2% at 24 weeks. These results appear to be significant milestones in the development of pemvidutide for MASH treatment.

Despite the positive news, the stock's pre-market decline suggests that investors may be adopting a "sell the news" strategy, where positive expectations were already priced into the stock. Alternatively, the market might be reacting to undisclosed aspects of the trial results or broader market trends affecting biotech stocks. As trading progresses, investors will be closely watching for any further clarification from the company or analyst interpretations that might explain the disconnect between the positive trial results and the stock's performance.