Safety of MVA-BN in Healthcare Personnel, Democratic Republic of the Congo

BackgroundModified vaccinia Ankara-Bavarian Nordic (MVA-BN) is a third generation, replication- deficient, smallpox and mpox vaccine prepared in liquid and lyophilized formulations. The Democratic Republic of the Congo reports the highest number of cases of clade I mpox annually. MethodsDuring the summer of 2017 and 2019, 1,600 healthcare personnel were enrolled in an investigational prospective cohort study to evaluate safety of the 2-dose MVA-BN vaccine series; 1000 were administered liquid and 600 were administered reconstituted lyophilized MVA-BN. Vaccine doses were given on study days 0 and 28 and presence or absence of adverse events were evaluated at routine follow-up appointments for up to two years. ResultsThere were 49% of liquid and 54% of lyophilized formulation participants who experienced at least one adverse event within 7 days. Eighteen serious adverse events, including seventeen deaths and one stillbirth, occurred within the 2-year study period; safety monitors deemed none were causally associated with vaccine administration. Fourteen pregnancies occurred within one month of vaccination, 13 gave birth to healthy infants. ConclusionsThis study adds to the growing body of literature on the safety of MVA-BN in different populations. The data from this Congolese cohort demonstrate good safety outcomes for up to two years with both liquid and lyophilized vaccine formulations. As MVA-BN vaccination campaigns are launched in endemic and surrounding countries in late 2024 as part of clade I mpox outbreak response efforts, the data from this study supporting safety of MVA-BN in an African population are crucial to build vaccine confidence. Trial registry number: NCT02977715