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Tecovirimat Shows No clinical Benefit for Mpox in NIH-Sponsored Trial
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Published: Wednesday, March 12, 2025
NIH-sponsored trial data offer further evidence to help inform mpox treatment decisions. The international study,presented at the 2025 Conference on Retroviruses and Opportunistic Infections (CROI) in San francisco,found that tecovirimat,when used alone,did not significantly reduce the time to clinical resolution of mpox lesions or improve pain control among adult patients. The trial, known as the Study of Tecovirimat for Mpox (STOMP), was halted in late 2024 after an interim analysis showed the ineffectiveness of tecovirimat monotherapy.
San Francisco, CA – in a important development for mpox treatment strategies, an international clinical trial sponsored by the National Institutes of Health (NIH) has revealed that the antiviral drug tecovirimat, when administered without othre antivirals, did not significantly reduce the time to clinical resolution of mpox lesions or improve pain control among adult patients. The findings were presented at the 2025 Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco,providing critical data for informing future mpox treatment strategies.
The trial,formally known as the Study of Tecovirimat for Mpox (STOMP),was initiated in September 2022 as part of a thorough U.S. government response to the clade II mpox outbreak. Tecovirimat, also known as TPOXX, is FDA-approved for the treatment of smallpox, a closely related virus. Though,its efficacy against mpox had not been rigorously studied in humans until this trial and a complementary study,PALM007,conducted in the Democratic republic of the Congo.
The STOMP trial was halted in late 2024 after an interim analysis indicated the ineffectiveness of tecovirimat monotherapy within the studied population. This decision underscores the importance of ongoing data analysis and adaptive trial designs in medical research.
This study brought us a step forward in better understanding mpox disease and potential treatment strategies.
Jeanne Marrazzo, M.D., M.P.H., director of NIH’s National Institute of Allergy and Infectious Diseases (NIAID)
Dr. Marrazzo further emphasized the importance of the research, stating, We are grateful to the study team and participants for their contributions to groundbreaking research on a disease that we still do not know enough about.
The NIAID sponsored and funded the trial, highlighting the NIH’s commitment to addressing emerging infectious diseases.
Study Design and Key Findings
The STOMP trial was a randomized,blinded,international efficacy study conducted across multiple countries,including Argentina,Brazil,Japan,Mexico,Peru,Thailand,the united States,and puerto Rico. This broad geographic depiction aimed to provide a comprehensive understanding of tecovirimat’s effectiveness across diverse populations.
Participants, who had experienced mpox symptoms for fewer than 14 days, were randomly assigned to receive either a 14-day course of tecovirimat or a placebo. Children, pregnant women, individuals with certain skin conditions, or those with significantly suppressed immune systems were assigned to an open-label arm, where all participants received tecovirimat. This open-label arm allowed researchers to gather data on the drug’s effects in vulnerable populations.
Participants in the randomized arms reported experiencing mpox symptoms for a median of eight days prior to entering the study and had a median of nine mpox lesions. Approximately one-third reported severe pain.By day 29, clinical resolution was observed in an estimated 83% of participants receiving tecovirimat, compared to 84% receiving the placebo – a difference that was not statistically notable. Similarly, improvements in pain scores were comparable between the two groups, with average pain scores decreasing by 3.2 points in the tecovirimat group and 3.1 points in the placebo group.
Viral load assessments revealed that at day eight, 48% of participants receiving tecovirimat had undetectable viral DNA, compared to 37% receiving the placebo. However, this difference narrowed by day 15, with 82% in the tecovirimat group and 80% in the placebo group showing undetectable viral DNA. Again,these differences were not statistically significant. Adverse event rates were also similar between the two randomized study arms.
These findings align with those from the PALM007 study in the Democratic Republic of the Congo, which also reported that tecovirimat did not significantly improve mpox resolution. The consistency of these results across different studies and populations strengthens the conclusion that tecovirimat monotherapy is not effective for treating mpox.
Implications and Future Research
An exploratory analysis of data from STOMP’s open-label arm sought to identify factors associated with faster mpox lesion resolution in participants at higher risk of severe mpox.The analysis indicated that younger age and the absence of HIV, or viral suppression in individuals living with HIV, were associated with faster clinical resolution.However, these associations were not significant when considering the duration of symptoms before study entry.
These findings suggest that while certain factors may influence the course of mpox, the timing of treatment initiation may be a critical determinant of outcomes. Further research is needed to identify specific biomarkers that can predict disease severity and guide treatment decisions.
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.
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
Dr. Wilkin further noted, Taken together, these latest results also highlight that we still have yet to isolate which factors influence mpox disease progression and clinical resolution.
mpox is caused by a virus that spreads primarily through close contact.While a clade II virus subtype caused a global outbreak in 2022, a clade I outbreak in Central and East African countries was declared a public health emergency of international concern in 2024. While travel-related cases of clade I mpox have been reported in the United States, the overall risk to the U.S. population remains low.Individuals with compromised immune systems, certain skin conditions, children, and pregnant women are at higher risk of developing severe mpox.
Study Details and Funding
The STOMP study was conducted by the NIH-funded ACTG, a global clinical trials network focused on HIV and other infectious diseases. SIGA Technologies, Inc., based in New York, provided tecovirimat for the study. The results will also be published in a scientific journal.
For more details about the STOMP trial, visit ClinicalTrials.gov using the identifier NCT05534984.
Mpox Treatment: Tecovirimat’s Effectiveness Questioned – An Expert Interview
“The recent NIH-sponsored STOMP trial delivered a surprising result: the antiviral drug tecovirimat showed no notable clinical benefit for mpox in adult patients. This challenges established understandings of mpox treatment strategies and necessitates a reassessment of current approaches.”
Mpox treatment Revolution: Tecovirimat’s Failure – Expert Insights
“The recent NIH-sponsored STOMP trial delivered a surprising result: the antiviral drug tecovirimat showed no notable clinical benefit for mpox in adult patients. This challenges established understandings of mpox treatment strategies and necessitates a reassessment of current approaches.”
Interviewer (Senior Editor, world-today-news.com): Dr.Anya Sharma, a leading virologist and infectious disease specialist, welcome to world-today-news.com. The recent STOMP trial results regarding tecovirimat’s efficacy against mpox have sent shockwaves through the medical community. Can you break down the key findings for our readers in simple terms?
Dr. Sharma: Certainly. The STOMP trial, a large, well-designed study sponsored by the NIH, investigated the effectiveness of tecovirimat, also known as TPOXX, as a monotherapy for mpox. The crucial finding is that tecovirimat, when used alone, did not significantly reduce the time to recovery from mpox lesions or alleviate pain in adult patients. This contradicts earlier assumptions about its potential as a first-line treatment. Essentially, the drug showed little to no added clinical benefit compared to a placebo.
Interviewer: This is quite a departure from what many expected. Given tecovirimat’s success against smallpox, a closely related virus, why might this be the case? What are the potential underlying reasons for its ineffectiveness against mpox?
Dr. Sharma: That’s a very insightful question. While smallpox and mpox share viral lineage, their interactions with the human immune system differ subtly. Smallpox has historically caused more profound and widespread systemic effects, making it more susceptible to antiviral interventions. Mpox, while serious, may involve different viral mechanisms of replication and immune response, rendering tecovirimat less effective. Moreover, the specific viral clade involved – in this case, Clade II – could influence the drug’s performance. It’s not simply a matter of using an “old solution for a new problem.” Further research is needed to understand the nuances of these viral-host interactions. We must explore the potential for genetic variability impacting drug susceptibility.
Interviewer: The trial also involved an open-label arm including vulnerable populations. What insights did this part of the study provide into mpox treatment and care?
Dr. Sharma: The open-label arm included children, pregnant women, and immunocompromised individuals who all received tecovirimat. This was particularly valuable because it allowed researchers to collect data on the safety and potential effects in populations often underrepresented in clinical trials.While the primary results showed no meaningful benefit for adults receiving the antiviral treatment, the open-label arm could provide valuable data on safety and pharmacokinetics. Future analyses of this data may reveal whether the drug might have a role in specific, high-risk patient subgroups.
Interviewer: What are the implications of these findings for current and future mpox treatment strategies? Does this mean we are back to square one?
Dr. Sharma: Absolutely not. The STOMP trial is a valuable stepping stone in understanding mpox treatment. While it highlights tecovirimat’s limitations as monotherapy, it doesn’t negate the importance of further research. One implication is the need to explore combination therapies or option antiviral agents. This is vital to identify more effective strategies in patients who exhibit more severe mpox symptoms or are at increased risk for complications. Supporting this need, the trial emphasizes the critical need for early diagnosis and supportive care remain cornerstones of mpox treatment.
Interviewer: What’s the next step? What research areas shoudl be prioritized to improve mpox treatment and management?
Dr. Sharma: Research must focus on several crucial areas. First, we need to explore why tecovirimat, shown to be effective against smallpox, failed to show clinical benefit for mpox in this study. This needs inquiry into the viral and host factors that determine treatment response. Second, we need to develop and test other antiviral drugs and combination therapies. This will involve identifying new drug targets and assessing their effectiveness in preclinical and clinical settings. research should focus on identifying biomarkers for predicting disease severity in order to better personalize mpox healthcare.
Interviewer: Thank you, Dr. Sharma, for shedding light on this crucial topic. This information will be invaluable for our readers.
Dr. Sharma: You’re welcome. It’s critically important to remember that scientific understanding is an iterative process and further research will likely refine our approach to treating mpox. With continued collaboration and dedication to research, we are moving closer to effective treatments. Let’s continue the conversation – share your thoughts in the comments below!