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Detection of Community Transmission of Clade Ib Mpox Virus in the United States
Eric C Tang1, Monica Haw1, Sonali Kulkarni2
1California Department of Public Health, Richmond, CA, USA.
Abstract:
AbstractA clade Ib mpox virus (MPXV) outbreak in Central and Eastern Africa has led to multiple travel-associated infections. In October 2025, clade Ib MPXV infection was confirmed in three unvaccinated, hospitalized men in California reporting no international travel. Phylogenetic analysis revealed clustering of these three MPXV infections with one recent travel-associated MPXV infection. This report provides evidence for local transmission of clade Ib MPXV in the Americas, occurring among gay, bisexual, and other men who have sex with men and their social networks.
Insights
Local mpox virus (MPXV) transmission is occurring in the Americas. Three unvaccinated men in California were infected with clade Ib MPXV, with genetic links to a travel-associated case, indicating community spread.
Area of Science:
- Epidemiology
- Virology
- Public Health
Background:
- Clade Ib mpox virus (MPXV) outbreaks have been documented in Central and Eastern Africa, with travel-associated cases reported globally.
- Recent mpox virus (MPXV) infections in unvaccinated individuals without international travel history raise concerns about local transmission.
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