According to a recent study done in Ontario, Canada, the smallpox vaccine from Bavarian Nordic A/S offers a reasonable level of protection against mpox infection. A single dose of the vaccine provided approximately 58% protection against monkeypox, according to research conducted between mid-June and late-October 2022.

The study is significant as it provides insight into the vaccine’s effectiveness amid a global health emergency triggered by a potentially more virulent clade Ib monkeypox virus strain identified in central Africa last month. Bavarian Nordic’s vaccine, known as MVA-BN, Imvamune in Canada, and Jynneos in the US, was originally developed to combat smallpox, a closely related disease. However, mpox, caused by the monkeypox virus, had not been evaluated in randomized controlled trials, which are considered the gold standard for determining a vaccine’s effectiveness.

Researchers pointed out that in the absence of such trials, their findings contribute valuable evidence supporting the vaccine’s role in preventing mpox infection. The study adds to the existing body of research that has observed effectiveness rates for the vaccine ranging from 36% to 86% across different populations.

During the early stages of the mpox outbreak in Ontario, a dose-sparing approach was implemented due to vaccine supply limitations, leading to initial single-dose administration. A two-dose regimen, which is the standard protocol approved in Canada, commenced on September 30, 2022. However, the study could not assess the effectiveness of the two-dose regimen as only a limited number of individuals had received the second dose by the end of the study period.

The findings from this study underscore the importance of making the vaccine available to at-risk communities and further investigating its effectiveness in preventing mpox, especially given the evolving nature of the virus and ongoing global health concerns.