The antiviral drug tecovirimat used without other antivirals did not reduce the time to clinical resolution of clade II mpox lesions or improve pain control among adults in an international clinical trial sponsored by the National Institutes of Health (NIH).
The trial enrollment was stopped in late 2024 when an interim analysis showed that tecovirimat monotherapy was ineffective in the study population. Detailed results were last week at the Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco.
The Study of Tecovirimat for Mpox (STOMP) began in September 2022 as part of the U.S. whole-of-government response to the clade II mpox outbreak. There are no mpox treatments approved in the United States. Based on animal studies, tecovirimat, also known as TPOXX, was approved by the Food and Drug Administration (FDA) to treat smallpox—a disease caused by a virus closely related to, but typically causing disease far more serious than, the virus that causes mpox. The drug had not been studied in people with mpox until the STOMP trial and a complementary study called PALM007 in the Democratic Republic of the Congo. PALM007 reported findings in 2024 that were similar to the findings reported from STOMP.
“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” said 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. “Taken together, these latest results also highlight that we still have yet to isolate which factors influence mpox disease progression and clinical resolution.”
Study Outcomes
Randomized participants in STOMP reported experiencing mpox symptoms for a median of eight days before study entry and had a median of nine mpox lesions. About a third of participants reported severe pain, selecting scores of 7-10 on an 11-point scale. By day 29 following study entry, an estimated 83% of participants receiving tecovirimat had reached clinical resolution, compared to 84% who received a placebo, a non-significant difference.
A separate exploratory analysis of data collected in STOMP’s open-label arm before the study had closed aimed to determine whether any factors were associated with faster mpox lesion resolution in participants with or at elevated risk of severe mpox. Faster clinical resolution was observed in participants who were younger in age or who did not have HIV or were living with HIV but virally suppressed on antiretroviral therapy; however, no association was significant when considering the duration of symptoms before study entry.
Source: National Institutes of Health