WHO says monkeypox vaccine ‘not a silver bullet’ as breakthrough cases reported 

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The World Health Organization said Wednesday that the monkeypox vaccine is not a “silver bullet,” with the health body beginning to receive reports of breakthrough cases after people have received the vaccine.

“The fact that we’re beginning to see some breakthrough cases is also really important information because it tells us that the vaccine is not 100 percent effective in any given circumstance, whether preventive or post-exposure,” said Rosamund Lewis, the WHO’s technical lead for monkeypox.

“We have known from the beginning that this vaccine would not be a silver bullet, that it would not meet all the expectations that are being put on it.” 

The only approved vaccine for monkeypox is from developer Bavarian Nordic and is being used as both a preventative vaccine, as well as to protect people recently exposed to the virus. Monkeypox, which spreads through close physical contact, was declared last month by the WHO to be a public health emergency of international concern.

There is limited data on the efficacy of the vaccine, and what is available has been drawn from animal studies. The main study used to indicate efficacy dates back to the 1980s and looked at a different type of smallpox vaccine — potentially more powerful than the safer vaccines that have since been developed. That study showed 85 percent protection against monkeypox.

Lewis said that new reports of breakthrough cases made it clear that the vaccine won’t prevent all cases of monkeypox. Other interventions remain vital, including reducing the number of sex partners in groups at the greatest risk, and giving time for the vaccine to generate a maximum immune response — typically two weeks after the second dose. 

The WHO has called for international studies to be set up during this global outbreak to generate the vaccine efficacy data that is currently lacking.