Drop in mpox cases examined

Changes in behaviour were probably the key reason for the stemming of the mpox outbreak in England last year, according to a new analysis.

Professor Peter Vickerman of the University of Bristol, UK, and colleagues wrote in Lancet Infectious Diseases that: “The 2022 global outbreak of mpox (formerly known as monkeypox) spread primarily among gay, bisexual, and other men who have sex with men.

“Understanding its epidemiological characteristics and the reasons for its downturn in July 2022 will help to control future outbreaks.”

They examined anonymous data on all 3,621 diagnosed mpox cases in England from May to November 2022, with 75 cases being used to estimate the incubation period.

A number of mathematical models were tested for how well they illustrated transmission, and the most suitable was used to show which changes led to the outbreak’s downturn.

Results showed that 98% of the cases occurred in men, and the median incubation period was seven days.

About 84% of the infections resulted from sexual partnerships with people at high risk of mpox, and the outbreak downturn was probably due to a 45% reduction in the sexual partner rate in this group.

Together with a 20% reduction in the effective infectious period, this prevented an estimated 165,896 infections.

A vaccine was introduced for high risk people in June 2022, this was estimated to have “marginally” reduced infections, “but minimised a resurgence in cases from January 2023” and is likely to “minimise future outbreaks”.

Professor Vickerman said: “Reductions in sexual risk behaviour among GBMSM at high risk of mpox, together with prompt diagnosis and isolation of people with mpox, can reduce the spread of an mpox outbreak to low levels.”

Zhang, X-S. et al. Mathematical modelling of the transmission dynamics and impact of control measures in the 2022 outbreak of mpox among gay, bisexual and other men who have sex with men in England. Lancet Infectious Diseases 11 September 2023; doi: 10.1016/S1473-3099(23)00451-6


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