Two Years On: MVA-BN Vaccine Still Shields Against Severe Mpox, But Equity and Boosters Loom as Next Frontiers
September 3, 2025
A new study in The Lancet Primary Care offers the strongest evidence yet that the MVA-BN vaccine provides durable protection against severe mpox more than 18 months after vaccination. Australian researchers found full vaccination reduced hospitalization risk by 89 percent, despite antibody levels waning within months. Breakthrough infections were milder, underscoring the vaccine’s continued clinical value. The absence of outcome data for HIV-positive individuals remains a critical gap, especially as outbreaks intensify in high-prevalence regions. Policymakers now face key questions: whether booster doses are needed, how to prioritize high-risk populations, and how to ensure global equity in vaccine access.
A retrospective cohort study in The Lancet Primary Care has delivered important reassurance: the MVA-BN vaccine continues to protect against severe mpox nearly two years after immunization. Conducted during Australia’s largest outbreak, the study found that fully vaccinated individuals had an 89 percent reduced risk of hospitalization and significantly fewer systemic symptoms. Even as antibody titers waned within months, clinical protection persisted, highlighting the distinction between laboratory markers of immunity and real-world outcomes.
The study also found fewer extragenital lesions among vaccinated individuals, a positive sign for reducing casual-contact transmission. However, a slight increase in anogenital lesions was observed, though these were typically mild and non-hospitalizing. Importantly, viral sequencing revealed no genetic divergence between viruses infecting vaccinated and unvaccinated people, suggesting vaccine escape is not driving breakthrough infections.
A major limitation is the lack of stratified data for people living with HIV. This omission is significant given the elevated risk of severe mpox among immunocompromised individuals, particularly those with low CD4 counts or uncontrolled infection. In sub-Saharan Africa, where HIV prevalence remains high, this represents an urgent research gap.
Beyond clinical findings, the study has broad public health implications. By preventing hospitalizations and systemic disease, vaccination reduces strain on health systems and supports resilience. The results also raise questions about booster strategies. Should individuals with advanced HIV, or those at high behavioral risk, be prioritized for additional doses?
The commentary accompanying the study underscores two imperatives: first, equitable access to vaccines for populations in lower-income countries facing resurgent outbreaks; and second, continued investment in sexual health clinics and broader community vaccination hubs to overcome disparities.
As mpox moves toward endemicity, the durability of MVA-BN is welcome news. Yet preparedness now hinges on refining booster policies, closing gaps for vulnerable populations, and ensuring global equity in vaccine distribution.