Dynamic Landscape of Mpox Importation Risks Driven by Heavy-Tailed Sexual Contact Networks Among Men Who Have Sex With Men in 2022

Abstract

Background: During the 2022 global mpox outbreak, the cumulative number of countries reporting their first imported case quickly rose in the early phase, but the importation rate subsequently slowed down, leaving many countries reporting no cases by the 2022 year-end.

Methods: We developed a mathematical model of international dissemination of mpox infections incorporating sexual networks and global mobility data. We used this model to characterize the mpox importation patterns observed in 2022 and to discuss the potential of further international spread.

Results: Our proposed model better explained the observed importation patterns than models not assuming heterogeneity in sexual contacts. Estimated importation hazards decreased in most countries, surpassing the global case count decline, suggesting a reduced per-case risk of importation. We assessed each country's potential to export mpox cases until the end of an epidemic, identifying countries capable of contributing to the future international spread.

Conclusions: The accumulation of immunity among high-risk individuals over highly heterogeneous sexual networks may have contributed to the slowdown in the rate of mpox importations. Nevertheless, the existence of countries with the potential to contribute to the global spread of mpox highlights the importance of equitable resource access to prevent the global resurgence of mpox.

Keywords: depletion of susceptible; global spread; importation risk; mpox; sexual contact networks.

Figure 1.

Number of countries reporting their first mpox case. The cumulative number of countries reporting their first mpox case by date of reporting (A) and date of symptom onset (B). Geographical regions are shown by colors. When the symptom onset date of the first case is unavailable, its imputed distribution is used to show all potential dates.

Figure 2.

Time-varying importation hazard of mpox cases. Estimated time-varying importation hazard of mpox in countries that have reported mpox importation events (A) and countries that have not (B), as of 1 October 2022. The best model accounting for selective depletion effect and region-specific scaling factors was applied to compute the time-varying importation hazard, and it was shown as a color scale. Dots and triangles indicate the reported and the median of the imputed symptom onset dates of the first confirmed mpox case in each country, respectively. The colors of dots and triangles represent the regions in which each country is located.

Figure 3.

Comparison of the regional-average importation hazard of mpox cases by model. Time-varying regional-average importation hazards of mpox cases in all regions (A) and less affected regions (Asia, Africa, Middle East, and Oceania) (B). Solid lines are the fitted importation hazard using the best model accounting for selective depletion effect and region-specific scaling factors. Dashed lines are the modeled one in the counterfactual scenario where the sexual network heterogeneity was assumed to be negligible (no selective depletion).

Figure 4.

Cumulative reported mpox cases and the estimated export capacity. Cumulative number of reported mpox cases (A and B) and the estimated export capacity (C and D) with a 2-month interval from 15 July to 15 September 2022. Countries shown in gray are either those where mpox cases existed prior to the current global outbreak or those where international travel volume data were unavailable in United Nations World Tourism Organization 2019 outbound tourism data.