Tecovirimat Fails to Improve Key Mpox Outcomes in Phase 3 Trial

Key Takeaways

• Tecovirimat was reported as not outperforming placebo on key mpox outcomes in this randomized phase 3 study.
• The trial enrolled 412 participants, used 2 to 1 randomization, and compared 14 days of tecovirimat with placebo across multiple countries.
• Rates of higher-grade adverse events and treatment discontinuation were described as similar between groups, and the authors emphasized that additional randomized controlled trials remain important for identifying safe and effective mpox therapeutics.

In CIDRAP’s summary of the New England Journal of Medicine publication, tecovirimat was reported as not providing measurable benefit over placebo in a phase 3 randomized study of adults with clade 2 mpox. Across the primary assessed outcomes, the comparison did not show improvement in clinical resolution, lesion healing, pain reduction, or viral DNA clearance. Investigators characterized the finding as negative for efficacy in this trial population.

The study randomly assigned 412 participants in a 2 to 1 ratio to tecovirimat or placebo for 14 days. Of those randomized, 344 had confirmed clade 2 mpox, and the trial was conducted across 49 sites in several countries.

Authors reported that efficacy measures tracked closely between groups across the assessed endpoints. At 29 days, clinical resolution and skin lesion resolution occurred at similar rates in both arms. The study also observed no significant differences in pain reduction, complete lesion healing, or viral DNA becoming undetectable.

Safety findings were presented separately and were described as broadly comparable between groups. Rates of grade 3 or higher adverse events were similar in participants receiving tecovirimat and placebo. Treatment discontinuation occurred at the same rate in each arm, and the report did not highlight a differential safety signal.

Investigators interpreted these results as evidence that the trial did not demonstrate added clinical benefit for tecovirimat over placebo in clade 2 mpox. They emphasized that randomized studies remain central to identifying therapies that are both safe and effective for mpox. Their discussion stayed focused on what this comparison did not establish, rather than implying a treatment role.