Effectiveness of JYNNEOS vaccine against symptomatic mpox disease in adult men in Los Angeles County, August 29, 2022 to January 1, 2023.

We describe real-world estimates of JYNNEOS vaccine effectiveness (VE) against symptomatic mpox in Los Angeles County (LAC). We conducted a retrospective cohort study of men aged ≥18 years residing in LAC who were at risk for mpox and eligible for the JYNNEOS vaccine from 5/19/2022 to 1/1/2023. Case demographics and route of JYNNEOS administration were obtained through vaccine administration data systems. HIV and sexually transmitted infection (STI) status was obtained through disease reporting systems for HIV and STI diagnoses in LAC. To estimate VE, we calculated weekly incidence of confirmed mpox for unvaccinated, partially vaccinated (episode date ≥14 days after first dose), and fully vaccinated (episode date ≥14 days after second dose) cohorts starting on 8/29/2022, when fully vaccinated coverage exceeded 3 %, and ending on 1/1/2023. Overall, 2,171 men had confirmed mpox, and 1,002 (46 %) of those were persons living with diagnosed HIV (PLWDH). 2,019 (93 %) mpox cases were unvaccinated, 114 (5 %) were partially vaccinated and 38 (2 %) were fully vaccinated. VE was 69 % (95 % CI 59-77) for partially vaccinated and 84 % (95 % CI 80-87) for fully vaccinated individuals. Among PLWDH, VE was 72 % (95 % CI 57-82) for fully vaccinated and 28 % (95 % CI -96 to 73) VE for partially vaccinated individuals. Among persons not living with diagnosed HIV, VE was 88 % (95 % CI 86-90) for fully vaccinated and 80 % (95 % CI 76-83) for partially vaccinated individuals. Of 111 individuals hospitalized with mpox, one was partially vaccinated, and the remaining were unvaccinated. Our results align with other published studies that reported that two doses of the JYNNEOS vaccine provided significant protection against symptomatic mpox.