A recent study from Ontario, Canada, has revealed that Bavarian Nordic A/S’s smallpox vaccine, marketed as Imvamune in Canada and Jynneos in the US, was 58% effective in preventing mpox infections after a single dose.
The research, conducted between mid-June and late October 2022, focused on gay and bisexual men, the group most affected during the global outbreak triggered by the clade IIb strain of the monkeypox virus.
The findings come as health experts seek to understand the vaccine’s effectiveness, particularly in light of a global health emergency declared after the emergence of the more dangerous clade Ib strain in central Africa.
While the vaccine was developed to combat smallpox, a related virus, it has not undergone randomized clinical trials—the gold standard for pharmaceutical evaluations—specifically for mpox.
Despite the lack of these trials, the study strengthens existing evidence that the MVA-BN vaccine offers protection against mpox.
The researchers from the Canadian Immunization Research Network Provincial Collaborative Network emphasized that the vaccine should be made widely available to high-risk communities.
Previous studies have shown an effective range of 36% to 86% in various populations, but this Ontario-based research focused on individuals who had received only a single dose due to initial supply limitations.
Ontario began administering a two-dose regimen on September 30, 2022, but the study could not assess the effectiveness of the second dose, as few individuals had received it by the end of the research period.
“Given the moderate effectiveness of a single dose, achieving high coverage with a full course could be important to prevent and manage ongoing transmission globally and prevent a large resurgence,” the researchers noted.
Experts suggest that while a single dose provides moderate protection, ensuring high coverage with the full course is essential to prevent further outbreaks and manage ongoing transmission globally.
What you should know
The World Health Organization (WHO) has authorized Gavi, the Vaccine Alliance, and UNICEF to begin procuring vaccines to combat mpox, despite the Emergency Use Listing (EUL) decision still pending. This move is intended to expedite vaccine distribution to affected regions and prepare for a comprehensive response once the EUL decision is finalized.
The WHO is expected to decide on the EUL for the mpox vaccine following recent data submissions by vaccine manufacturers. The EUL process helps expedite the evaluation and authorization of medical products during public health emergencies.
The U.S. government donated 10,000 doses of the mpox vaccine to Nigeria. These vaccines will be administered primarily to those at high risk, including close contacts of confirmed cases and frontline healthcare workers, with provisions for reactive vaccination in other states as necessary.
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