Preliminary reports on monkeypox vaccinations suggest the vaccine is not 100 percent effective, and some breakthrough cases are occurring, the World Health Organization said during an Aug. 17 media briefing.
In some cases, breakthrough infections are occurring in people vaccinated after a monkeypox exposure, which is intended to reduce disease severity. The breakthrough cases should not come as a surprise, as the WHO was not expecting 100 percent efficacy, according to Dr. Rosamund Lewis, the organization'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, and that we don't have firm efficacy data or effectiveness data in this context," she said.
Dr. Lewis cited a limited study from the 1980s, which showed that smallpox vaccines used at the time were about 85 percent effective against monkeypox.
She said it's unclear what the current vaccine's overall efficacy will be, but still stressed the importance of vaccination to protect those at high risk.