Heavy-tailed sexual contact networks and the epidemiology of monkeypox outbreak in non-endemic regions, May 2022

A global outbreak of monkeypox across non-endemic regions including Europe and North America was confirmed in May 2022. The current outbreak has shown distinct epidemiological features compared with past outbreaks in non-endemic settings, most notably its observed rapid growth and predominant spread among men who have sex with men (MSM). We use a branching process transmission model fitted to empirical sexual partnership data in the UK to show that the heavy-tailed nature of the sexual partnership degree distribution, where a small fraction of individuals have disproportionately large numbers of partners, can explain the sustained growth of monkeypox cases among the MSM population despite the absence of such patterns of spread in past outbreaks. We also suggest that the basic reproduction number (R0) for monkeypox over the MSM sexual contact network may be substantially greater than 1 for a plausible range of assumptions, which poses a challenge to outbreak containment efforts. Ensuring ongoing support and tailored public health messaging to facilitate prevention and early detection among MSM with a large number of sexual partners is warranted.