Data from a recent trial sponsored by the National Institutes of Health (NIH) offers fresh insights into treatment strategies for mpox. The study focused on the antiviral tecovirimat, which was administered as monotherapy to adults infected with clade II mpox. However, results indicated that the drug did not significantly reduce the time to clinical resolution of lesions or enhance pain management compared to placebo. Enrollment in the trial ceased in late 2024 following an interim analysis that demonstrated its ineffectiveness in this context. Findings were unveiled at the 2025 Conference on Retroviruses and Opportunistic Infections held in San Francisco.
As part of an international effort to understand mpox better, researchers embarked on a randomized efficacy study known as STOMP (Study of Tecovirimat for Mpox). This endeavor commenced in September 2022 during the global outbreak of clade II mpox. Participants included individuals from Argentina, Brazil, Japan, Mexico, Peru, Thailand, and the United States who had been symptomatic for less than 14 days. To ensure unbiased results, both participants and investigators were unaware of whether they received tecovirimat or a placebo. Special consideration was given to vulnerable populations such as children, pregnant women, and those with compromised immune systems, ensuring they all received tecovirimat under an open-label arm.
The evaluation centered around the safety of tecovirimat and its effectiveness in reducing visible lesion duration while improving other outcomes like pain relief. Despite showing promise in animal studies against smallpox, tecovirimat's performance in human mpox cases fell short. By day 29 post-study entry, approximately 83% of participants receiving tecovirimat achieved clinical resolution versus 84% in the placebo group—a statistically insignificant difference. Pain scores also improved similarly between the two groups.
In addition to clinical observations, viral DNA presence in lesion swabs was monitored throughout the study period. At day eight, nearly half of the tecovirimat recipients exhibited undetectable viral DNA levels compared to one-third among placebo users; however, these differences diminished by day 15. Adverse event occurrences remained comparable across both randomized arms.
A separate exploratory analysis within the open-label arm sought correlations between faster lesion resolution and various factors such as age, HIV status, and symptom duration prior to enrollment. Although younger participants without HIV or those managing HIV effectively showed quicker recovery trends, no significant associations emerged when accounting for pre-enrollment symptom durations.
Despite these findings, the STOMP trial remains pivotal in guiding future research directions. It underscores the necessity for further investigation into identifying key determinants influencing mpox disease progression and clinical resolution. According to Timothy Wilkin, M.D., M.P.H., chief of the Division of Infectious Diseases and Global Public Health at UC San Diego, understanding these nuances is crucial moving forward.
This landmark study conducted through NIH-funded ACTG highlights the complexities surrounding mpox treatment and emphasizes the need for continued exploration. Collaborative efforts involving stakeholders like SIGA Technologies, Inc., will undoubtedly play a vital role in advancing our knowledge base and developing effective interventions against this challenging virus.