Short-Lived Neutralizing Antibody Responses to Monkeypox Virus in Smallpox Vaccine-Naive Persons after JYNNEOS Vaccination.

JYNNEOS, a third-generation smallpox vaccine, is integral to monkeypox virus (MPXV) control efforts, but the durability of this modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine's effectiveness is undefined. We optimized and used a plaque reduction neutralization test (PRNT) with authentic clade IIa MPXV and vaccinia virus to assess antibody responses over 12 months in 8 donors vaccinated with 2 doses of JYNNEOS. One donor previously received the ACAM2000 vaccine; 7 donors were smallpox vaccine-naive.