Study Observed No Clear Benefit of Tecovirimat in Clade II Mpox Patients: NEJM

A new study published in The New England Journal of Medicine revealed that the antiviral drug tecovirimat did not significantly improve recovery outcomes among adults infected with the clade II strain of mpox. The findings raise important questions about the drug’s role in managing mpox outbreaks and may influence future treatment guidelines.

Tecovirimat was initially developed as a treatment for smallpox, it received approval from the U.S. Food and Drug Administration under the Animal Rule. The approval of the drug relied heavily on studies in nonhuman primates infected with viruses related to mpox. However, evidence of effectiveness in humans has remained limited.

Thus, this new phase 3 clinical trial involved 412 participants from multiple countries who had suspected mpox infections. Of these, 344 were confirmed to have clade II mpox, which was the strain responsible for the global outbreaks starting in 2022 and monitored by the World Health Organization.

The participants were randomly assigned in a 2-to-1 ratio to receive either oral tecovirimat or a placebo for 14 days. The primary outcome of the study was to determine whether the drug shortened the time needed for clinical resolution (healing of active skin or mucosal lesions). Secondary outcomes included pain reduction, complete lesion healing, viral DNA clearance, and overall safety.

By day 29, clinical resolution occurred in approximately 83% of patients who received tecovirimat and 84% of the patients who received placebo. Similarly, tecovirimat did not significantly reduce pain levels among participants reporting severe discomfort at the start of the study. Rates of complete lesion healing and viral clearance were also similar between the treatment and placebo groups.

4% in the tecovirimat group and 3% in the placebo group faced some serious adverse events, which suggests thar the drug remains generally well tolerated even if its effectiveness is uncertain.

Tecovirimat therapy did not shorten the disease duration, reduce pain, or accelerate viral clearance in adults with clade II mpox. The findings suggest that routine use of the drug for otherwise uncomplicated cases may provide limited clinical benefit. Overall, the findings highlight the need for continued research into effective mpox treatments, particularly for patients at higher risk of severe disease. 

Source:

Zucker, J., Fischer, W. A., II, Zheng, L., McCarthy, C., Saha, P. T., Javan, A. C., Greninger, A., Hamill, M. M., Leslie, K., Brooks, K. M., Berardi, J., Smith, D., Hosey, L., Aldrovandi, G., Ferbas, K., Day, C., Bender Ignacio, R. A., Bolan, R., Glesby, M. J., … Wilkin, T. (2026). Tecovirimat for the treatment of mpox. The New England Journal of Medicine, 394(9), 884–895. https://doi.org/10.1056/nejmoa2506495