People who were eligible for a monkeypox vaccine but did not receive one were about 14 times more likely to become infected than those who were vaccinated, according to preliminary data released Wednesday by the Centers for Disease Control and Prevention (CDC).
While extremely limited, the figures offer an initial look at the effectiveness of the Jynneos vaccine in the real world.
“These new data provide us with a level of cautious optimism that the vaccine is working as intended,” CDC Director Rochelle Walensky told reporters.
But the numbers are based on data collected from just 32 states, and there’s no way to distinguish how much of a reduction in cases is due to the vaccine alone, and how much is due to behavioral changes among the most at-risk populations.
The data is also based on people who received just a single dose of the vaccine. According to the CDC, relatively few individuals in the current outbreak have completed the recommended two-dose series.
Infections continue to decline week over week, but there are currently more than 25,000 cases of monkeypox identified across all 50 states.
Health officials have seen protection from monkeypox for those vaccinated with Jynneos as early as two weeks after the first dose, Walensky said. Still, she said laboratory studies show that immune protection is highest two weeks after the second dose of vaccine, so they are continuing to strongly recommend people get two doses of Jynneos spaced out 28 days apart.
“What we have right now is data on how well our vaccine is working after a single dose. What we don’t yet have is what happens after a second dose and how durable that protection is,” Walensky said.
In addition to initial numbers, health officials on Wednesday said they are expanding eligibility for the Jynneos vaccine by moving to a pre-exposure prophylaxis strategy.
The new strategy “encourages vaccine providers to minimize the risk assessments of people seeking the vaccine. Fear of disclosing sexuality and gender identity must not be a barrier to vaccination,” said White House monkeypox adviser Demetre Daskalakis.
Daskalakis said people who might be at present or future risk are now eligible, including: gay, bisexual and other men who have sex with men; transgender or gender diverse people who have had more than one sex partner in the last six months; had sex in a place associated with higher monkeypox risk, or had a sexually transmitted infection diagnosed in the past six months.
The strategy also extends vaccines to sexual partners of people at risk and commercial sex workers, Daskalakis said.