Difference in the efficacy of the modified-vaccinia Ankara vaccine as pre-exposure and post-exposure prophylaxis against sexual transmission of monkeypox virus clade IIb in non-human primates

The monkeypox virus (MPXV) outbreak of 2022 caused a human disease with unusual epidemiological and clinical features, notably an increase in human-to-human transmission through sexual contact, predominantly among men who have sex with men (MSM). This evolution underscores the need to reassess prevention and control strategies in the context of a sexually transmitted disease. Here, we show that rectal challenge of cynomolgus macaques with a 2022 clade IIb MPXV isolate mimics sexual transmission, leading to rectal infection, with systemic and male genital tract dissemination and seminal fluid shedding. Vaccination with modified-vaccinia Ankara (MVA) protected the macaques from subsequent rectal MPXV challenge. However, MVA failed to prevent the disease when administered four days post-exposure to MPXV. These findings have a critical impact on outbreak management and highlight the importance of reevaluating MVA post-exposure prophylaxis protocols.