NIH Trial Finds Tecovirimat Ineffective As Monotherapy For Mpox

SIGA Technologies’ SIGA antiviral drug tecovirimat, when used without other treatments, did not reduce the time for clade II mpox lesions to heal or significantly alleviate pain, according to results from an international clinical trial sponsored by the National Institutes of Health (NIH).

The study, known as STOMP, was halted in late 2024 after an interim analysis indicated the drug was ineffective in the study population.

Mpox has two identified variants: clades I and II. A clade II outbreak in 2022 led to global transmission, with continued low-level circulation.

Meanwhile, a clade I outbreak in Central and East Africa was declared a public health emergency in 2024.

STOMP launched in September 2022 as part of a U.S. government initiative addressing the clade II mpox outbreak.

No mpox-specific treatments have been approved in the U.S.

Tecovirimat, also known as TPOXX, was originally authorized by the FDA to treat smallpox based on animal studies but had not been evaluated in humans with mpox before STOMP and a parallel study, PALM007, conducted in the Democratic Republic of the Congo.

PALM007 yielded similar results from STOMP, further questioning tecovirimat's effectiveness for mpox.

Results showed that by day 29, 83% of participants taking tecovirimat had achieved clinical resolution, compared to 84% in the placebo group, indicating no meaningful difference.

Among those who reported severe pain at the study's outset, pain reduction was similar across groups, with tecovirimat users reporting an average decrease of 3.2 points on an 11-point scale, compared to 3.1 points for placebo recipients.

Viral DNA levels declined over time in both groups, with no statistically significant differences at key checkpoints.

Adverse event rates were also comparable between treatment and placebo groups.

A separate exploratory analysis examined STOMP's open-label participants—those at higher risk of severe mpox. The analysis found that younger participants and those without HIV or with well-controlled HIV experienced faster lesion resolution.

However, no strong correlation was observed between symptom duration before study entry and recovery speed. Researchers noted that open-label participants had fewer lesions but slower recovery compared to PALM007 trial participants.

On Tuesday, SIGA Technologies reported fourth-quarter earnings of 63 cents, down from $1.01, and sales of $81.4 million, down $116.5 million from a year ago.

Price Action: SIGA stock is up 7.05% at $6.02 at the last check Wednesday.

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