The CDC, however, has begun to release data related to the former vaccine. The agency found unvaccinated patients were approximately 14 times more likely to become infected with the virus based on early real-world effectiveness data.
In the week of August 28, monkeypox incidence was 230 per 100,000 for unvaccinated individuals. Among those who received at least one dose of the Jynneos vaccine in the same period, 15 per 100,000 became infected.
Although the U.S. government has made the ACAM2000 vaccine available for use against monkeypox, it remains unclear how protective it is in the current outbreak.
Because data continue to be limited, CDC has counseled people who have received either vaccine to take other precautions to avoid infection.
A recent research letter published in JAMA analyzes monkeypox infections after a single dose of the Jynneos vaccine in the U.S. Midwest.
The research, which considered 7,339 individuals who had received their first dose of the Jynneos vaccine, found that 400 patients tested positive for monkeypox. Of those who tested positive, 37.8% had HIV.
Most monkeypox infections occurred within two weeks after receiving the first dose of the vaccine — likely before full immunity could develop.
The authors also note that some of the infections “may not represent true vaccine failure because patients may have sought vaccination after realizing they were exposed.”
In some cases, the incubation period for monkeypox can be 17 days or more. However, one study found that the average incubation period was 8.5 days.
The JAMA study’s authors also reported at least two breakthrough infections in individuals at least three weeks after a second dose.
The authors note that more data are needed to understand vaccine effectiveness against monkeypox.
Filed Under: Infectious Disease