In a real-world study from Ontario, researchers confirmed that a single dose of the Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine offers 58% protection against mpox infection. Conducted between June and November 2022, the study tracked 9,803 men at high risk for mpox due to sexual behaviours or STI history. Vaccinated individuals experienced far fewer infections compared to unvaccinated counterparts. This research strengthens the evidence for MVA-BN’s moderate effectiveness and highlights the importance of completing the full vaccination regimen as mpox cases rise globally.
The study matched 3,204 vaccinated participants with 3,204 unvaccinated men, controlling for key confounding factors like age, geographical region, and HIV status. With only 71 mpox cases diagnosed over the study period, the vaccinated group showed significantly lower infection rates—0.09 per 1,000 person-days versus 0.20 per 1,000 person-days in the unvaccinated group.
The study design also incorporated sensitivity analyses, ensuring that the findings were robust despite the relatively small sample size. Previous studies have estimated vaccine effectiveness against mpox at between 36% and 86%, and the Ontario study’s results fit squarely within this range, further bolstering the case for the vaccine’s role in controlling future outbreaks. Importantly, the study also found that the MVA-BN vaccine’s effectiveness only becomes apparent after 14 days post-vaccination, indicating that early infection may not be preventable.
Although the study could not evaluate the impact of a second dose due to limited vaccine availability during the trial, it reinforces the importance of broader vaccination campaigns. With mpox cases rising again in 2024, these findings advocate for the rapid deployment of full-dose vaccination efforts to prevent further spread. As mpox continues to pose a public health risk, achieving high vaccine coverage will be essential in managing future outbreaks.
Disclosures: This article was created by the touchINFECTIOUS DISEASES team utilizing AI as an editorial tool (ChatGPT (GPT-4o) [Large language model]. https://chat.openai.com/chat.) The content was developed and edited by human editors. No funding was received in the publication of this article.
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