A cluster of drug-resistant mpox has been identified in five states, US officials report to Reuters

By Julie Steenhuysen

CHICAGO (Reuters) – U.S. health officials have identified a cluster of cases caused by a variant of mpox that is resistant to Siga Technologies’ antiviral tecovirimat, branded as TPOXX, in five U.S. states, federal and state researchers reported on Thursday .

The cases involved a total of 18 people infected with clade II mpox between Oct. 6, 2023, and Feb. 15, 2024, who had never taken the treatment before, according to the report published in the Centers for Disease Control and Prevention’s Morbidity and Prevention. Weekly Mortality Report.

Cases of Clade II mpox, which are endemic in West Africa, sparked a global outbreak in 2022 that prompted the World Health Organization to declare a public health emergency, and cases continue to spread at low levels in some countries.

The drug-resistant mpox cases follow an initial, unrelated cluster reported in California in late 2022-early 2023 and are the first to involve multiple states, according to the report.

Health officials said the most recent cases are likely to have been underestimated because not all mpox cases undergo genetic sequencing to determine the variant that causes the infection.

The study authors said routine surveillance to monitor the emergence of drug resistance is needed to protect the effectiveness of TPOXX, one of the few treatments approved for the treatment of mpox.

CDC officials advised doctors to closely follow the protocol for using TPOXX, make sure patients are taking the drug properly, and stress that they can spread the virus while taking the drug. The findings also underscore the need for additional treatments for mpox, the study authors said.

The Clade II strain is separate from the ongoing outbreak in Africa of a new variant called Clade Ib, which prompted the WHO to declare a second public health emergency in August.

A US government-backed study evaluating the use of TPOXX in Clade Ib cases released in August showed that the treatment was not effective in helping patients recover faster than an inactive treatment.

Mpox, formerly known as monkeypox, is a viral infection that causes flu-like symptoms and pus-filled lesions. Although usually mild, the virus can be fatal in some people with weakened immune symptoms. Mpox is transmitted through close physical contact, including sexual contact.