The World Health Organization (WHO) last week reported that breakthrough infections of monkeypox have occurred after vaccination—suggesting that more precautions may be necessary to reduce the spread of the virus in the current outbreak.

WHO reports breakthrough monkeypox infections

In a media briefing on Aug. 17, WHO announced preliminary reports of breakthrough monkeypox infections among people who had been vaccinated—suggesting that the vaccine is not 100% effective against infection from the virus.

According to Rosamund Lewis, WHO’s technical lead for monkeypox, the breakthrough cases are not a surprise. “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,” Lewis said

“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,” she added

So far, much of the data on the monkeypox vaccine is from a retrospective analysis published in 1988.

A retrospective analysis? If I’m not mistaken the retrospective analysis is based on previous information. Of a type that may or may not be specifically related to the present day topic

“Retrospective research often requires the analysis of data that were originally collected for reasons other than research”

In addition, immunological studies in humans have shown that the vaccine generates monkeypox antibodies in people’s blood—but the level of protection is not currently known.

Although these outbreaks are “far from extinguished,” there are signs that “they’re a bit more under control than they had been” in some areas, said Donald Vinh, an infectious disease specialist at McGill University.

However, Vinh noted that it’s too soon to determine whether the vaccine is the primary factor contributing to the decline in monkeypox cases in these countries. “No single measure is going to really be the solution here.”

In addition to vaccination, people at high risk are recommended to take precautions to protect themselves from infection. For example, WHO earlier this month recommended “reducing your number of sexual partners, reconsidering … sex with new partners, and exchanging contact details with any new partners to enable follow up if needed.”