The US National Institutes of Health (NIH) has announced that Siga Technologies’ antiviral drug, tecovirimat, was safe but failed to improve mpox resolution or pain.
The Study of Tecovirimat for Mpox (STOMP) assessed tecovirimat among adults with mild to moderate clade II mpox and a low risk of developing severe disease.
Interim data from this international trial showed that the drug failed to demonstrate efficacy in reducing the time to skin and mucosal lesion resolution or influencing pain.
Based on these findings, the study’s Data Safety and Monitoring Board (DSMB) recommended halting further participant enrolment for te covirimat or placebo.
NIH’s National Institute of Allergy and Infectious Diseases (NIAID), as the study sponsor, accepted this recommendation.
Due to the lack of efficacy signal, NIAID also closed enrolment in an open-label study arm for participants at elevated risk of severe disease, which was not designed to assess the drug’s efficacy.
Tecovirimat, also known as TPOXX, was developed in partnership with the US government and approved initially by the US Food and Drug Administration (FDA) to treat smallpox. However, the drug’s safety and efficacy for treating mpox were not established until this year.
In 2022, the antiviral drug was approved in the UK for the treatment of smallpox, monkeypox, cowpox, and vaccinia complications.
The STOMP findings align with results from a NIAID-cosponsored trial of tecovirimat among children and adults with clade I mpox in the Democratic Republic of the Congo, reported earlier this year.
NIAID director Jeanne Marrazzo said: “The initial STOMP findings provide valuable insight to inform clade II mpox medical countermeasures and underscore the critical importance of conducting well-designed randomised clinical trials during infectious disease outbreaks.”
STOMP was launched in September 2022 as part of the US response to the clade II mpox outbreak.
An interim analysis at 75% of the study’s target enrolment showed no difference in lesion resolution time between participants treated with tecovirimat and those receiving a placebo.
Siga Technologies CEO Diem Nguyen said: “The STOMP results are not unexpected as the study design was similar to the PALM007 study except it was in patients with mild to moderate clade II mpox compared to patients with clade I mpox.
“It is important to note that approximately 75% of mpox patients in the randomised arms of the STOMP trial received tecovirimat more than five days after symptom onset, and higher risk patients were included in an open-label arm.”
Further analyses of the study data are ongoing.
