Risk assessment of human mpox infections: retrospective cohort study

The global supply of vaccines against mpox (previously called monkeypox virus infection) was significantly lower than the demand. Therefore, evidence-based vaccine prioritization criteria, based on risk assessment were needed. Our objective was therefore to identify the characteristics of individuals at the highest risk for mpox.

This population-based cohort study included all Clalit Health Services (CHS) subjects assumed to be at risk for mpox. The eligibility criteria for inclusion were determined based on known characteristics of people with infection worldwide and insights of lesbian, gay, bisexual, transgender, queer+ (LGBTQ+) -specialized CHS clinicians. Cox hazards models were used to identify the risk factors for mpox within the study cohort. The study commenced on 6 June 2022, the date of the first known mpox in CHS members, until 31 July 2022, when the mpox vaccination campaign started.

A total of 8088 individuals of 4.7 million CHS members (0.18%) were identified according to the study inclusion criteria. Of those, 69 (0.85%) developed infection during the study period. Risk factors for mpox were birth in 1980 or later (hazard ratio, 5.04; 95% CI, 2.11-12.02), history of syphilis (2.62; 1.58-4.35), registration to primary healthcare clinics in the Tel Aviv district (2.82; 1.44-5.54), HIV-pre-exposure prophylaxis medication use (3.96; 2.14-7.31), PDE5 inhibitors use (2.92; 1.77-4.84), and recent sexually transmitted infections (STIs) within the last 18 months (2.27; 1.35-3.82). No infections were observed in individuals with none of the factors. Individuals with three or more risk factors had a 20.30-fold (10.39-39.69) higher risk for mpox compared with those with 0-2, with 85.5% (75.0-92.8%) sensitivity and 77.8% (76.9-78.7%) specificity.

Weighting individuals' risk levels based on validated risk factors against vaccine availability can assist health systems in the equitable prioritization of vaccine allocation in various future outbreaks, given supply-demand gaps.