Impact of interventions on mpox transmission during the 2022 outbreak in Canada: a mathematical modeling study of three different cities

Abstract

AbstractBackgroundThe 2022-2023 global mpox outbreak primarily affected gay, bisexual, and other men who have sex with men (GBM). It was met with swift community and public health responses. The relative impact of GBM’s reductions in sexual partners, contact tracing/isolation, and vaccination on transmission in Canadian cities remain unknown.MethodsWe estimated changes in sexual behaviours during the outbreak using 2022 data from theEngage Cohort Studywhich recruited self-identified GBM in Montréal, Toronto, and Vancouver (n=1,445). The numbers of sexual partners in the past 6 months (P6M) were modeled using negative binomial regressions. A transmission-dynamic compartmental model was calibrated to surveillance data. We estimated the averted fraction of new infections attributable to reductions in sexual partners, contact tracing/isolation, and first-dose vaccination, versus an unmitigated epidemic scenario, in each of the three cities.ResultsThe empirical estimates of sexual behaviours changes were imprecise: 20% (RR=0.80; 95% credible intervals [95%CrI]: 0.47-1.36) fewer sexual partners among those reporting ≤7 partners (P6M) and 33% (RR=0.67; 95%CrI: 0.31-1.43) fewer among those with >7 partners (P6M). Compared to the unmitigated epidemics, we estimated that the three interventions combined avert 46%-58% of cases. Reductions in sexual partners, contact tracing/isolation prevented approximately 12% and 14% of cases, respectively. Vaccination’s effect varied across cities by start date and coverage, with 21%-39% mpox infections prevented.ConclusionsReduction in sexual activity, contact tracing/isolation, and vaccination all contributed to accelerating epidemic control and infections averted. Early vaccination had the largest impact.