Sexual behavior modification as well as natural immunity due to infection were the main drivers of the decline of the 2022-2023 mpox outbreak primarily among men who have sex with men (MSM) in Europe and the United States, according to a new study in The Lancet Infectious Diseases.
The study is based on results from a cross-sectional online survey conducted in 23 countries in Europe and the Americas from May 19 to May 31, 2023. The survey was advertised on four dating apps used by affected communities. In the final analysis, 16,875 respondents were included in the study.
Most of the participants were men (95.3%) who identified as either gay (80.4%) or bisexual (16.5%). Overall, vaccination with at least one dose of Jynneos was reported by 4,987 participants (29.6%); 3,502 (20.8%) reported two doses. A total of 6.4% of respondents reported having had mpox during the outbreak.
Fewer sex partners
Half of the participants (50.9%) said they changed their sexual behavior during the outbreak, and 35.5% said they continued to do so through May 2023. The most common changes made were reducing their number of sexual partners (93.2%), avoiding group sex (88.4%), and avoiding sex-on-premises venues (84.6%).
Participants who received one or two doses of vaccine, however, were less likely to report also changing their sexual behavior, as were those who reported a previous infection with the virus. Behavior modification was strong in North America and Latin American countries, and weaker in western Europe, the authors said.
“Given stark vaccine inequity but similar reductions in transmission rates between regions during the first year of the global response, our study supports the hypothesis that the sudden decline in MPXV clade IIb transmission seen at the end of 2022 was primarily due to a combination of behavioral adaptation and naturally acquired immunity,” the authors concluded.
Findings not relevant for current outbreak
In a commentary on the study, two Dutch experts said the findings confirm that vaccines had a limited role in ending the global mpox outbreak. Moreover, the data are not relevant to the current expanding and worrisome clade 1b outbreak in Africa.
“Currently, MSM are not among the most vulnerable populations in this outbreak; instead, children (<15 years) account for 66% of cases and 82% of mpox-related deaths in DR Congo,” they write. “Behaviour modulation in children could be challenging.”
Moreover, a significant number of clade 1b infections occur among sex workers, who are unlikely to change their behavior and jeopardize their income.
The differences between this outbreak and the global 2022–23 outbreak among MSM underline the urgent need for mpox vaccination.
“The differences between this outbreak and the global 2022–23 outbreak among MSM underline the urgent need for mpox vaccination,” they write. “Addressing the mpox crisis will require a multifaceted approach that ensures equitable access to vaccines and health-care services, enhances surveillance and diagnostic capacities, and increases investment in research to enhance our understanding of viral evolution and its effect on the shifting epidemiology of mpox.”
