ACTG Presents Data from Mpox Study STOMP at CROI

Associated Press

12-03-2025

LOS ANGELES, March 12, 2025 (GLOBE NEWSWIRE) -- ACTG, a global clinical trials network focused on HIV and other infectious diseases, recently presented data demonstrating that tecovirimat did not improve mpox resolution. The results from STOMP (Study of Tecovirimat for Mpox, also known as A5418) were shared as the oral abstracts, 'Tecovirimat is Safe but not Efficacious in People with Clade II Mpox' and 'Host and Disease Factors Were Not Associated with the Resolution of Mpox in Participants Receiving Tecovirimat' at the 2025 Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco, California. STOMP stopped enrolling participants in December 2024 after an interim analysis showed that the treatment did not reduce the time to lesion resolution or have an effect on pain among adults with mild to moderate clade II mpox and a low risk of developing severe disease.
'The results from STOMP reinforce the value of randomized clinical trials during outbreaks of infectious diseases, like mpox,' said Past ACTG Chair Judith Currier M.D., M.Sc. 'There was considerable hope that tecovirimat would be an effective mpox treatment and it was only through this rigorously designed trial that we were able to conclusively demonstrate that tecovirimat alone did not speed time to resolution of mpox.'
STOMP was a phase 3, randomized, placebo-controlled, double-blind trial evaluating the safety and efficacy of tecovirimat for the treatment of mpox. Tecovirimat (SIGA Technologies, Inc.) is approved by the U.S. Food and Drug Administration (FDA) to treat smallpox, but prior to STOMP it was not yet known if it could effectively or safely treat mpox. STOMP was initiated in September 2022 in response to a global outbreak of mpox that was characterized by increased person-to-person transmission. Mpox continues to circulate in the United States and around the world and there are no therapies that have been shown to be effective.
STOMP enrolled participants who had had symptoms of mpox for less than 14 days and randomized them to receive either tecovirimat (600 mg) or a placebo twice daily for 14 days. Participants with or at risk for severe disease, pregnant women, and children were enrolled in an open-label arm in which everyone received tecovirimat.
Tecovirimat is Safe but Not Efficacious in People with Clade II Mpox
Today's presentation, which was highlighted in a CROI press conference, found that tecovirimat did not reduce the time to clinical resolution of mpox lesions or improve pain control among adults with clade II mpox. There were no safety concerns and no deaths in either arm.
STOMP randomized 412 eligible participants to tecovirimat (275) and placebo (137) at 50 sites in seven countries. Among those participants, 24 percent were enrolled remotely, 98 percent were male, 53 percent were White, 11 percent were Black, and 45 percent were Hispanic. 33 percent were living with HIV and 22 percent had received at least one dose of an mpox vaccine.
'Importantly, STOMP showed that we can quickly design and execute international clinical trials in the face of an ongoing pandemic,' said Protocol Chair Timothy Wilkin, M.D., M.P.H., University of California San Diego. 'It will be necessary, based on today's results, to pursue alternative treatments for mpox and other orthopoxviruses.'
Host and Disease Factors Were Not Associated with the Resolution of Mpox in Participants Receiving Tecovirimat
This presentation analyzed a number of host and disease-related factors, including age, HIV status, vaccination status, and duration of symptoms, that might be associated with clinical mpox resolution and when mpox DNA was no longer detectable in skin lesions among the study participants who were enrolled in the open-label arm of STOMP. This analysis did not identify predictors of clinical mpox resolution and researchers suggested further investigation of this topic.
While there were trends between younger age and lower levels of mpox DNA with faster clinical resolution, researchers found no significant associations in multivariate modeling (a statistical technique that determines the contributions of a number of factors to a singular outcome) with either clinical resolution or clearance of mpox DNA.
'In the setting of public health emergencies, clinical trials like STOMP play an important role in not only evaluating treatments for safety and efficacy, but also potentially identifying key risk factors associated with worse outcomes,' said STOMP Vice Chair and Lead Author William Fischer, M.D., University of North Carolina. 'The data presented here represent an important step forward in the evaluation of tecovirimat and in our understanding of mpox.'
STOMP was led by Dr. Wilkin, Dr. Fischer, Jason Zucker, M.D., Columbia University (Vice Chair), and Dr. Currier. ACTG is led by Joseph J. Eron, M.D., UNC (ACTG Chair) and Rajesh T. Gandhi, M.D., Massachusetts General Hospital and Harvard Medical School (ACTG Vice Chair). It is sponsored by the National Institutes of Health's (NIH) National Institute of Allergy and Infectious Diseases (NIAID, which also funds ACTG) under award numbers UM1 AI068636, UM1 AI107716, and UM1 AI068634.
ACTG is the world's largest and longest running clinical trials network focused on HIV and other infectious diseases and the people living with them. It is funded by NIAID and collaborating NIH Institutes. Founded in 1987, ACTG conducts research to improve the management of HIV and its comorbidities; develop a cure for HIV; and innovate treatments for tuberculosis, hepatitis B, and emerging infectious diseases. It comprises thousands of dedicated researchers, staff, and community members who are pursuing research into novel treatments and cures for infectious diseases at 65 locations across four continents, with the ultimate goal of advancing science that meaningfully impacts the lives of the people we serve.