IntroductionA key part of the response to the mpox (monkeypox) epidemic has been the vaccination campaign targeted at gay, bisexual and other men who have sex with men (GBM), including people living with HIV (PLWH).MethodsWe undertook a single-site, retrospective analysis of individuals who received a single dose of modified vaccinia Ankara (MVA-BN) prior to the onset of mpox symptoms. Demographics, clinical characteristics and patient management were analysed.ResultsOf 10 068 individuals who received a first dose of the MVA-BN vaccination, 15 (0.15%) developed mpox subsequently. All individuals identified were GBM with 12/15 (80%) on Pre-exposure prophylaxis (PrEP) and 3/15 (20%) PLWH. Median time from MVA-BN inoculum to mpox symptoms was 4 days (IQR 3–9), systemic symptoms and supportive medical treatment required were common (11/15 patients, 73%) and all had localising skin lesions. One individual required hospitalisation.ConclusionsAlthough clinical presentation was similar to unvaccinated cohorts, we observed low numbers of mpox cases following a first dose of MVA-BN vaccination. Larger, multicentric studies are needed to further evaluate vaccination failure and immunity duration.