Mpox, a single dose of vaccine effective in 58% of monkeypox cases: the research

A single dose of the anti-Mpox vaccine – formerly monkeypox – from the Danish Bavarian Nordic (Modified vaccinia Ankara-Bavarian Nordic, Mva-Bn) is 58% effective in protecting against the infection that the World Health Organization has again declared an international public health emergency, due to fears related to the rapid spread of a new viral strain in Africa. This is what emerges from a Canadian study published in ‘Bmj’ by researchers from the Ices (Institute for Clinical Evaluative Sciences) – Public Health Ontario and the Map Centre for Urban Health Solutions at St. Michael’s Hospital of Unity Health Toronto.

In 2022, during the Mpox outbreak, Ontario introduced the vaccine as a protective measure for people at high risk of contracting the infection. “The initial vaccination campaign used a single dose to reach as many at-risk people as possible,” explains Christine Navarro of Public Health Ontario, lead author of the study. “We used real-world health data to estimate the effectiveness of the Mpox vaccine as rigorously as possible,” adds Jeff Kwong, senior scientist at ICES. The study enrolled adult men with a history of testing for syphilis and a sexually transmitted bacterial infection (STI) in the previous year, or who had been prescribed HIV prevention medications. Eligible vaccine recipients were matched to unvaccinated recipients matched by age, area of ​​residence, prior HIV or STI diagnoses, and other non-Mva-Bn vaccines received, and infection rates in the 2 groups were compared to determine the effectiveness of the Mpox vaccine.

A total of 3,204 males vaccinated with Mva-Bn and the same number of unvaccinated were included. During the follow-up, 21 Mpox infections were diagnosed in the vaccinated group and 50 in the unvaccinated group. Hence the calculation: “The estimated efficacy of a single dose of Mva-Bn vaccine against infection was 58%”. Comments Sharmistha Mishra, infectious disease specialist at Ices and Map Centre: “The results of our study strengthen existing evidence that a single dose of the mpox vaccine is moderately effective against infection. The vaccine should be made rapidly available and accessible to at-risk populations, given the current public health emergency”.