A new study published in JAMA documents 90 monkeypox cases after one or two doses of the Jynneos vaccine—including 2 infections 3 weeks or more after two doses—among more than 7,000 vaccine recipients.

Most post-vaccination cases occurred shortly after the recipients had received only the initial dose of Jynneos vaccine, demonstrating full vaccine efficacy was not reached until 14 or more days after the second dose.

8 cases noted 1 month post-vaccine

In the study, which was completed in the Chicago area this summer, researchers tracked 90 people who tested positive for monkeypox after receiving Jynneos among 7,339 who got a first dose of the vaccine.

Of them, 69 (77%) tested positive for monkeypox within 14 days after their first dose. Another 21 got infected after 14 days, and 8 after 28 days. Only 2 people contracted monkeypox 3 weeks or more after receiving both doses.

The study authors don't specify how many people in the study received two vaccine doses, but six of the eight people who contracted monkeypox 29 or more days after the first dose had received a second dose.

Of the 90 vaccine recipients who tested positive for monkeypox, the median age was 33, 91% were cisgender men, and 36.8% were living with HIV.

Of the cases recorded 1 to 14 days after vaccination, 36.2% (25/69) involved people with HIV, of whom 96% (24/25) were virologically suppressed. Fifty-four percent (24/44) of early post-vaccination cases without HIV infection were using pre-exposure prophylaxis.

"Because the incubation period for monkeypox is 3 to 17 days, some of the cases occurring between 1 and 14 days after vaccination may not represent true vaccine failure because patients may have sought vaccination after realizing they were exposed," the authors concluded.

They added, "Of concern is that at least 2 breakthrough infections were observed in individuals at least 3 weeks after a second dose."

Read more...