By Julie Steenhuysen
CHICAGO (Reuters) – U.S. health officials have identified a cluster of cases in five U.S. states caused by an mpox variant resistant to Siga Technologies’ antiviral tecovirimat branded as TPOXX, federal and state investigators said on Thursday.
The cases involved a total of 18 people who were infected with clade II mpox between Oct. 6, 2023, and Feb. 15, 2024, and who had never previously received the treatment, according to the report published in the Centers for Disease Control and Prevention’s Morbidity and Prevention. Weekly mortality report.
Clade II mpox cases, which are endemic to West Africa, led to a global outbreak in 2022 that prompted the World Health Organization to declare a public health emergency, and cases remain at low levels in some countries spread.
The cases of drug-resistant MPox follow an initial, unrelated cluster reported in California in late 2022-early 2023, and are the first involving multiple states, according to the report.
Health officials said the latest cases are likely underestimates because not all cases of mpox undergo genetic sequencing to determine the variant causing the infection.
The study authors said routine surveillance is needed to monitor the emergence of drug resistance to ensure 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 TPOXX use, making sure patients take the drug properly and emphasizing that they can still spread the virus while taking the drug. The findings also underscore the need for additional MPOX treatments, 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 on the use of TPOXX in clade Ib cases, released in August, found that the treatment was not effective at helping patients recover faster than a dummy treatment.
Mpox, formerly known as monkeypox, is a viral infection that causes flu-like symptoms and pus-filled lesions. Although the virus is usually mild, it can be fatal in some individuals with weakened immune symptoms. Mpox is transmitted through close physical contact, including sexual contact.
