A LARGE multicentre study has confirmed the safety and moderate effectiveness of MVA-BN vaccination in preventing mpox infection among high-risk populations in Germany.
Amid the global mpox outbreak, which has surpassed 115,000 confirmed cases since 2022, third-generation smallpox vaccines such as modified vaccinia Ankara–Bavarian Nordic (MVA-BN) have been deployed for prevention, though clinical data have been limited. Researchers conducted the Safety and Effectiveness of MVA-BN Vaccination Against MPXV Infection (SEMVAc) and Emulated Target Trial for Effectiveness of MVA-BN Vaccination Against mpox Infection in At-risk Individuals (TEMVAc) studies to evaluate MVA-BN safety and real-world effectiveness. SEMVAc enrolled 6,459 men who have sex with men and transgender individuals with changing sexual partners. TEMVAc compared 3,027 vaccinated individuals with 3,027 matched unvaccinated controls, using Kaplan–Meier analysis to estimate effectiveness following one or two subcutaneous doses of MVA-BN.
The vaccine was well tolerated, with low adverse reaction rates (0.35% after the first dose; 0.14% after the second). Local and systemic reactions were more common after the first dose than the second. In the effectiveness analysis, 16 mpox cases occurred among vaccinated individuals versus 32 in the unvaccinated group. One-dose vaccine effectiveness after 14 days was 57.8% overall (95% CI: 11.8–83.0), 84.1% in people without HIV, and only 34.9% in those with HIV. Notably, breakthrough cases in vaccinated individuals were milder compared with those in the unvaccinated cohort.
This study supports MVA-BN as a safe and moderately protective intervention against mpox, although immunocompromised patients may need closer monitoring. Rapid data generation via hybrid trial designs may be crucial during emerging public health emergencies.
Reference
Safety and effectiveness of MVA-BN vaccination against mpox in at-risk individuals in Germany (SEMVAc and TEMVAc): a combined prospective and retrospective cohort study. Lancet Infect Dis. 2025; DOI:10.1016/S1473-3099(25)00018-0.
