Previous studies have observed an effectiveness rate ranging from 36 percent to 86 percent in different populations | Representational
Bavarian Nordic A/S’s smallpox vaccine was moderately effective at preventing mpox infection after a single dose, according to a study in Ontario, Canada, where the shot likely helped curb an outbreak in 2022.
Researchers in the study found that a single vaccination provided about 58 percent protection against mpox infection. It was conducted between mid-June and late October 2022 among gay and bisexual men, the group most affected during a global outbreak driven by the clade IIb strain of the monkeypox virus.
Health experts are trying to gauge the effectiveness of Bavarian Nordic’s MVA-BN vaccine (also known as Imvamune in Canada and Jynneos in the U.S.) and older inoculations after the spread of a potentially more dangerous clade Ib monkeypox virus strain in central Africa sparked a global health emergency last month. The vaccines, developed to protect against smallpox, a related disease, have not been evaluated for mpox in randomized controlled trials, the gold standard for assessing a pharmaceutical’s effectiveness.
“In the absence of randomized clinical trials, our findings strengthen the evidence that MVA-BN is effective in preventing mpox infection and should be made available and accessible to at-risk communities,” scientists from the Canadian Immunization Research Network Provincial Collaboration Network said in the study, published Wednesday in The BMJ.
Previous studies have observed an effectiveness rate ranging from 36 to 86 percent in different populations, the researchers said.
Although Imvamune is approved in Canada as a two-dose series 28 days apart, Ontario initially employed a dose-sparing strategy where patients initially received one dose due to supply issues.
A two-dose regimen was started there on September 30, 2022. But researchers could not estimate the efficacy of two doses because only a few people had received a second dose by the end of the study period.
“Given the moderate efficacy of a single dose, achieving high coverage with a full regimen could be important to prevent and manage ongoing transmission globally and avoid a major resurgence,” they said.
First published: September 12, 2024 | 8:53 am IS
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