Monkeypox vaccine not 'a silver bullet,' WHO says, as breakthrough cases emerge

As demand for monkeypox vaccines increases, the World Health Organization (WHO) has begun to receive preliminary reports on the efficacy of the shots, which suggests there are breakthrough cases occurring, officials said Wednesday.

"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, and that we don't have firm efficacy data or effectiveness data in this context," officials said during a press conference.

Some of the reports of breakthrough cases have been among people who received a prophylaxis vaccine after exposure.

"The fact we're beginning to see some breakthrough cases is also really important information because it tells us that the vaccine is not 100% effective in any given circumstance. Whether preventive or post-exposure, we cannot expect 100% effectiveness at the moment based on this emerging information," officials said.

This occurrence of breakthrough infections is not new, officials noted, explaining that a limited study from the 1980s demonstrated that the vaccines offered about 85% protection against monkeypox.

"[The] vaccine is not a silver bullet," officials said, "that every person who feels that they're at risk and wishes to lower their own level of risk [has] many interventions are at their disposal, which includes vaccinations where available, but also includes protection from activities where there may be a risk -- reducing [the] number of sex partners, avoiding group sex or casual sex, and, specifically, when a vaccine is, in fact, administered, waiting until that vaccine has the time to produce a maximum immune response."

Earlier this month, the Biden administration announced it would move forward with a plan to increase the U.S. monkeypox vaccine supply by as much as five times, using an injection method that requires less vaccine per shot.

Across the country, federal data shows that more than 634,000 doses of the JYNNEOS vaccine have been shipped to states and jurisdictions as of Aug. 12.

The number of monkeypox cases identified across the globe continues to grow, with the total jumping by 20% in the last week, according to the WHO.

Globally, more than 38,000 cases of monkeypox have now been confirmed, according to the CDC, including more than 13,500 cases in the U.S.

The majority of cases, in the current monkeypox outbreak, have been detected in gay, bisexual or other men who have sex with men. However, health officials have repeatedly stressed that anyone can contract the virus.