Monkeypox epidemics may have subsided even before mass vaccinations, as members of vulnerable groups have developed herd immunity. This has been reported by the European Society for Clinical Microbiology and Infectious Diseases.
A monkeypox epidemic occurred in 2022. This disease has been known for a long time, but there are no cases of persistent transmission of the pathogen from person to person. More than 85,000 cases have been reported worldwide, and men of unconventional sexual orientation and random sex are most at risk. In May 2023, the number of cases began to rise sharply, and an unexplained decline began a few months later.
Some researchers attributed this decline to vaccination, but the decline in smallpox cases in most countries, including Belgium, began before a significant portion of the population at risk was vaccinated. Christoph Van Dijk of the Institute of Tropical Medicine tested the hypothesis that this is due to a change in people’s behavior.
To find out, the authors reviewed questionnaires from people who presented to the clinic with monkeypox. Of these, 95% were gay men, and the average number of sexual partners in the previous three weeks was two. It turned out that by the end of the epidemic, the average number of sexual partners per week had dropped to about one. However, when people who did not have smallpox were surveyed who visited the clinic to receive PrEP, a way to reduce the risk of HIV transmission, it was found that the monthly number of sexual partners among them only increased.
“The decrease in the number of partners reported by people diagnosed with smallpox towards the end of the epidemic is indicative of a change in the behavior of risk groups. However, this was not supported by data on PrEP users, where the total number of sexual partners increased over time. Therefore, we propose an alternative hypothesis: the main members of the sexual network were first infected with monkeypox, then the peripheral ones. The infection-induced immunity of the people at the core of the network led to the collective immunity of the members, which stopped the epidemic,” the scientist summarizes.