In a study published yesterday in Eurosurveillance, a team led by Johns Hopkins University researchers describe an mpox clade 1b outbreak in Uvira, a densely populated city in the Democratic Republic of the Congo (DRC), where transmission was driven primarily by household contact rather than sexual exposure.
A second report in the same journal details sexual, household, and health care spread of clade 1b in Ireland’s first documented outbreak.
The clade 1b variant appeared in the DRC community of Kamituga in September 2023 and spread primarily through heterosexual contact. By mid-2024, the outbreak had spread to Uvira, some 230 miles away, and mostly affected children. From June to October 2024, clinicians recorded 973 suspected cases, nearly two-thirds (63.7%) of which occurred in children younger than 15 years.
Most reported exposures occurred within households (67.9%) with large family sizes and crowded living conditions. Sexual transmission accounted for only 6.0% of cases in Uvira. Among 439 respondents, one-quarter (24.6%) reported exposures in restaurants, bars, hotels and nightclubs, and 3.2% reported exposure in health care facilities.
Malnourished kids may be more vulnerable
Several key factors may explain the high rate of clade 1b among children, including greater susceptibility to mpox due to childhood malnutrition and existing smallpox immunity in adults.
Although the overall death rate was low (0.7%) in the Uvira-centered outbreak, it was 5.6 times higher in infants than in other age-groups, suggesting young children’s vulnerability in regions marked by malnutrition, limited access to health care, and crowded homes. The median household size in Uvira is eight people, with a median of four people sleeping in the same room.
Overall, however, the death rate for clade 1b in infants was lower than the death rate for young children during clade 1a outbreaks, which may reflect a reduced virulence of clade 1b.
The Uvira outbreak highlights a shift toward nonsexual transmission (though some sexual transmission likely persists), and addressing nonsexual transmission vectors in densely populated, resource-limited areas is challenging. The World Health Organization recommends home isolation to help prevent transmission, for example, but isolating can be costly and impractical for families in crowded households.
These realities showcase the need for household-level prevention strategies, argue the authors, such as vaccination, nutritional support, and targeted, community-level interventions.
Irish health worker infected while caring for patient
Mpox clade 1b also spreads in higher-income, higher-resource settings. A Eurosurveillance rapid communication, also published yesterday, details Ireland’s first known outbreak of clade 1b. The Irish cluster involved four epidemiologically linked cases from August to October 2025, including a health care worker infected while caring for a hospitalized patient.
The Irish outbreak originated with a traveler returning from Pakistan and spread via sexual, household, and nosocomial (in a healthcare setting) transmission. The cases were genetically identical and related to a sequence from Oman in February 2025. The close relationship between the Oman and Irish sequences highlights the role of international travel in the spread of clade 1b and the potential for global transmission.
Together, the two studies spotlight the international threat posed by mpox clade 1b. The authors emphasize the need for sustained surveillance, rapid diagnostics, and multi-organizational responses to prevent further spread.
