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A drug used in the last global mpox outbreak in 2022-23 is not effective against the more severe virus spreading rapidly in Africa, researchers have found.
The antiviral, tecovirimat, did not reduce the duration of lesions among children and adults with clade I mpox in the Democratic Republic of the Congo (DRC), according to the initial results of a placebo-controlled trial run by researchers in the DRC and the U.S.
Clade I is a more dangerous type of mpox — formerly known as monkeypox — than clade II which caused a global outbreak in 2022, and is associated with more severe illness and higher fatality rates. Clade I is disproportionately affecting children, a trend not seen in the 2022 outbreak, and triggered the World Health Organization to declare a global emergency on Wednesday.
“These findings are disappointing, but they give us essential information and reinforce the need to identify other therapeutic candidates for mpox while we continue research on tecovirimat use in other populations with mpox,” said Jeanne Marrazzo, director of the U.S. National Institute of Allergy and Infectious Diseases (NIAID).
The NIAID-backed study did show that deaths could be avoided when mpox patients were treated in hospital. Researchers enrolled 597 mpox patients who were all admitted to hospital for at least 14 days. The mortality rate — including those who received a placebo — was 1.7 percent, compared to at least 3.6 percent among all cases in the DRC, they said.
“This shows that better outcomes among people with mpox can be achieved when they are hospitalized and provided high-quality supportive care,” the National Institutes of Health statement said.
The manufacturer, SIGA, also noted that there was a “meaningful improvement” for those treated early and with the most severe disease. While not statistically significant, SIGA believes the data support further trials in these groups. SIGA’s share price fell more than 40 percent following the results, but had recovered about half as much by Friday afternoon.
Tecovirimat is approved in the EU for the treatment of smallpox and monkeypox but based only on animal studies. The authorization was granted under “exceptional circumstances” without the clinical efficacy data normally required.
The European Commission bought supplies of the drug during the 2022-23 outbreak, while authorities in the U.K. recommended it as an option for hospitalized patients. The U.S. also made the drug available to some mpox patients in 2022 as part of studies into its effectiveness.
