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The following is a summary of “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,” published in the March 2025 issue of Lancet Infectious Diseases by Hillus et al. 

The 2022 global outbreak of monkeypox virus (mpox), with over 1,15,000 confirmed cases and the emergence of clade I, prompted a Public Health Emergency of International Concern.  

Researchers conducted a retrospective study to assess the safety and effectiveness of the third-generation smallpox vaccine, modified vaccinia Ankara–Bavarian Nordic (MVA-BN), recommended for at-risk populations.   

They enrolled men who have sex with men and transgender individuals aged 18 years or older with changing sexual partners in Germany (Safety and Effectiveness of MVA-BN Vaccination Against MPXV Infection [SEMVAc]) from July 7, 2022, to Dec 31, 2023 and assessed the safety and reactogenicity of 1 and 2 doses of subcutaneous MVA-BN. Vaccine effectiveness was evaluated using risk ratios from the Kaplan–Meier estimator in (Emulated Target Trial for Effectiveness of MVA-BN Vaccination Against mpox Infection in At-risk Individuals [TEMVAc]). A total of 3027 vaccinated individuals were matched (1:1) with 3027 unvaccinated controls. The SEMVAc and TEMVAc were registered in the HMA-EMA Catalogue (EUPAS50093) and the German Clinical Trials Register (DRKS00029638) and have been completed.  

The results showed that 6,459 individuals were enrolled in SEMVAc. Adverse reactions were uncommon after the first dose (0.35% [95% CI 0.20–0.60]) and the second dose (0.14% [95% CI 0.06–0.33]). Local reactions were more frequent after the first dose (70.2% [95% CI 68.5–71.8]) than the second dose (56.8% [95% CI 54.6–59]), as were systemic reactions (first dose: 22.3% [95% CI 20.9–23.9]; second dose: 17.6% [95% CI 15.9–19.4]). In TEMVAc, 16 mpox cases occurred in vaccinated individuals, compared to 32 cases in matched unvaccinated individuals (median follow-up 55 days [IQR 23–89]). Vaccine effectiveness 14 days or later after 1 dose was 57.8% (95% CI 11.8–83.0) overall, 84.1% (95% CI 42.0–100) in individuals without HIV, and 34.9% (95% CI –72.8 to 79.0) in individuals living with HIV. Breakthrough infections in vaccinated individuals were associated with milder symptoms compared to infections in unvaccinated individuals.  

Investigators concluded that the MVA-BN vaccine was safe and provided protection against mpox, though with reduced effectiveness in people living with HIV. 

Source: thelancet.com/journals/laninf/article/PIIS1473-3099(25)00018-0/fulltext