Adaptive behavior in response to the 2022 mpox epidemic in the Paris region

The 2022 mpox outbreak saw a rapid case surge among men-who-have-sex-with-men (MSM) in previously unaffected regions, driven by heterogeneity in sexual networks. A sudden decline followed, but its drivers remain unclear as it is difficult to distinguish the roles of vaccination, herd immunity, and behavioral changes. We developed a network model of mpox transmission among MSM based on sexual behavior data and fitted it to the Paris region epidemic. We studied whether the decline was driven by post-exposure prophylaxis (PEP) vaccination, immunity among highly active MSM, or behavioral changes. Behavioral shifts were modeled as either uniform or based on individual risk factors, like sexual activity or exposure to diagnosed cases. We used the cross-sectional 2023 ERAS survey to validate findings. Behavioral changes adopted by 49% (95%CI 47-51%) of MSM regardless of individual risk factors best explained the observed epidemic decline. These changes prevented an estimated 73% (28-99%) of mpox cases in summer 2022. Findings aligned with the ERAS survey data, showing that 46% (45-48%) of MSM reduced sexual partners. On the contrary, PEP vaccination and immunity among highly active MSM were insufficient to curb the outbreak. Widespread behavioral change was the primary driver of the mpox epidemic decline in the Paris region, before preventive vaccination or immunity could affect epidemic spread. These findings highlight the importance of effective risk communication and community engagement in outbreak management. Tailored public health responses that encourage adaptive behaviors, especially as vaccination efforts ramp up, are essential for supporting affected communities.