A single dose of a smallpox vaccine seems to lower the risk of catching mpox by around 60 per cent, and two doses would probably be even better
By Christa Lesté-Lasserre
11 September 2024
There is little good-quality research into smallpox vaccines’ effectiveness against mpox
Emmanuele Contini/NurPhoto via Getty Images
Receiving a single dose of one type of smallpox vaccine seems to lower the risk of catching mpox by around 60 per cent, although this may vary depending on the variant of the virus.
Cases of mpox, formerly known as monkeypox, are surging in the Democratic Republic of the Congo, driven by a variant called clade Ib. The vaccines used to protect against mpox were originally developed for smallpox, and while the two viruses are related, their efficacy for mpox specifically is unclear.
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To learn more, Sharmistha Mishra at the Institute for Clinical Evaluative Sciences in Toronto, Canada, and her colleagues focused on a vaccine called MVA-BN, also known as JYNNEOS, Imvanex and Imvamune. This was the most widely used smallpox vaccine in Western countries during the 2022 mpox outbreak, which was caused by the clade IIb variant.
Research suggests that MVA-BN’s efficacy for mpox varies hugely, from 36 per cent to 86 per cent. That range could be due to the studies being observational and comparing the outcomes of people with different ages, locations and health statuses.
Randomised control trials are under way among gay, bisexual and other men who have sex with men, who made up the majority of infections in Western countries during the 2022 outbreak.