Background: Although modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccination is approved for smallpox and monkeypox prevention, immunological persistence and booster effects remain undescribed.
Methods: Participants naive to smallpox vaccination were randomized to 1 dose MVA-BN (1×MVA, n = 181), 2 doses MVA-BN (2×MVA, n = 183), or placebo (n = 181). Participants with previous smallpox vaccination received 1 MVA-BN booster (HSPX, n = 200).