MVA-BN third-dose 5 years after primary; Democratic Republic of the Congo

BACKGROUNDThe expanding mpox outbreak in Africa and travel-associated cases in other continents have sparked efforts to expand vaccination. In this study and the accompanying report (Minhaj et al.), we assess the safety and long-term immunological response of MVA-BN vaccination. METHODSIn 2022, five years after the primary MVA-BN series, a third (booster) dose was administered to healthcare workers in the Democratic Republic of the Congo (DRC). Adverse events were recorded on days 0, 7, and 14, and antibody response measured on days 0, 7, 14, and 545 following the third dose. Study documentation and surveillance records were examined to identify possible infections following the primary series. RESULTSAntibody kinetics indicative of an anamnestic response, with a rapid and massive increase in anti-Orthopoxvirus (OPXV)-specific IgG but not IgM, and a nearly 90-fold rise in OPXV-neutralizing antibody titers were observed by day 14. Anamnestic response was observed in all participants irrespective of their seropositivity at the time of booster vaccination with enhanced antibody levels through day 545. In comparison to primary vaccination, third dose participants had 4.2 greater odds of experiencing local reactogenicity, but no difference in systemic adverse events through day 7 post-vaccination. Finally, in five years following the primary series, only one confirmed case of mpox has been identified. CONCLUSIONMVA-BN vaccination induces sustained immunological memory after primary vaccination observed by rapid anamnestic response up to five years post-vaccination. Booster vaccination had increased reactogenicity compared to primary vaccination but enhances antibody durability.