NIH-Sponsored Study Confirms Ineffectiveness of Tecovirimat for Clade II Mpox
A recent National Institutes of Health (NIH) clinical trial has found that tecovirimat, an antiviral drug, is ineffective in treating clade II mpox.
While the drug remains safe, it did not speed up healing or improve pain control in patients. These findings could shape future mpox treatment strategies and guide clinicians toward better therapeutic options.
Ineffectiveness of Tecovirimat Confirmed
A 2024 interim analysis of the Study of Tecovirimat for Mpox (STOMP) revealed that tecovirimat monotherapy did not significantly reduce symptom duration or pain in individuals with clade II mpox.
The trial was conducted across multiple countries, including the United States, and was halted early due to lack of efficacy.
Conducted under NIH’s National Institute of Allergy and Infectious Diseases (NIAID), STOMP aimed to evaluate tecovirimat’s effectiveness in real-world clinical settings.
The findings, presented at the 2025 Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco, reaffirm previous results from the PALM007 study in the Democratic Republic of the Congo.
Trial Design and Participant Insights
The study enrolled 592 participants across the United States, Argentina, Brazil, Japan, Mexico, Peru, and Thailand. Participants were randomly assigned either tecovirimat or a placebo for 14 days.
The study included an open-label arm for high-risk patients, such as those with weakened immune systems, severe mpox, or certain preexisting conditions.
Findings at a Glance
| Measure | Tecovirimat Group | Placebo Group |
|---|---|---|
| Clinical Resolution by Day 29 | 83% | 84% |
| Pain Reduction (Avg. Points) | 3.2 | 3.1 |
| Undetectable Viral DNA (Day 8) | 48% | 37% |
| Undetectable Viral DNA (Day 15) | 82% | 80% |
What the Data Shows
- Tecovirimat did not significantly improve healing times or pain relief.
- Differences in viral clearance between groups were not statistically significant at any stage.
Expert Insights and Next Steps
Dr. Jeanne Marrazzo, Director of NIAID, emphasized that while the trial did not support tecovirimat use, it provided valuable data on mpox progression and treatment needs.
Timothy Wilkin, M.D., M.P.H., chief of the Division of Infectious Diseases and Global Public Health at the University of California, San Diego said:
“Since the start of the clade II outbreak, clinicians treating mpox have had limited evidence to guide their practice, and STOMP provided definitive answers on the lack of clinical utility of tecovirimat monotherapy for the randomized population studied.”
“Taken together, these latest results also highlight that we still have yet to isolate which factors influence mpox disease progression and clinical resolution.”
What This Means for Future Mpox Treatment
Currently, no FDA-approved treatments exist for mpox. While tecovirimat was authorized for smallpox, its role in mpox management remains uncertain. The NIH is expected to pursue alternative antiviral research to fill this treatment gap.
Final Thoughts
These findings reinforce the importance of evidence-based treatments for mpox. While tecovirimat may not be the solution, ongoing research will be crucial in developing effective therapeutic options.
Clinicians and health agencies must continue exploring new strategies to combat mpox infections.
More details about STOMP.
Sources: National Institutes of Health.
