Usefulness of Single Dose of Subcutaneous Modified Vaccinia Ankara for Human Monkeypox

Abstract The recent global outbreak of the human monkeypox virus was declared a public health emergency by the WHO. Modified Vaccinia Ankara (MVA), provided in a two-dose regimen, is currently the only FDA-approved vaccine against monkeypox virus infection (MPXVi). Nevertheless, many have implemented a single-dose strategy to maximize vaccine supply because of a vaccine shortage. The emergency approval of MVA use for MPXVi was based only on efficacy data from non-human primates. Evidence for the real-life effectiveness of MVA in reducing MPXVi is still warranted. This observational, retrospective cohort study included all members of Clalit Health Services (CHS), eligible for the MVA vaccine on Jul. 31, 2022, when the CHS vaccination campaign was initiated. The rate of MPXVi in participants who received one dose of MVA was compared with that for participants who were not vaccinated. A Cox proportional-hazards regression model with time-dependent covariates was used to estimate the association between vaccination and MPXVi while adjusting for sociodemographic and clinical risk factors. A total of 2,092 subjects met vaccine eligibility criteria. Of those, 1,068 (51%) were vaccinated during the 105 days study period and completed at least 25 days of follow-up. During the study period, 5 infections were confirmed in the vaccinated and 16 infections were confirmed in the unvaccinated participants. The adjusted vaccine effectiveness was estimated at 87% (95% CI: 60%-95%). Our results suggest that a single dose of subcutaneous MVA is associated with a significantly lower risk for MPXVi in high-risk individuals and may contribute to the containment of the current outbreak.