MVA-BN monkeypox vaccine safety in a clinical trial in the Democratic Republic of the Congo

Abstract The MVA-BN vaccine is considered safe and effective and has been widely deployed to prevent monkeypox. However, safety and tolerability data from endemic areas are limited. We performed a single-arm clinical trial of the safety of the MVA-BN vaccine among adults in the Democratic Republic of the Congo (ClinicalTrials.gov: NCT05734508; Registered 21 February 2023). Participants were personnel working on a monkeypox therapeutics trial (PALM-007) conducted in a high-risk, endemic setting for monkeypox. Participants received two doses of vaccine 28 days apart and were actively followed up to 28 days after each dose to assess the safety profile of MVA-BN. From March 2023 to June 2024, 500 participants were enrolled and received their first vaccine dose; 494 (99%) received the second dose and associated follow-up. There were no adverse events (AEs) of grade 3 or higher observed during the study. 175 participants (35%) reported at least one vaccination site AE, the most common of which was mild or moderate vaccination site pain (120/500 first dose recipients (24%); 48/494 second dose recipients (10%)). There was one recorded case of breakthrough monkeypox occurring approximately 3 months after the second dose. This observational study provides further evidence that the MVA-BN monkeypox vaccine is generally safe and well-tolerated. As previously reported, the most common AEs were mild or moderate injection site reactions.