Infections reported after single dose of monkeypox vaccine

Most cases of monkeypox that occur after vaccination with the modified Vaccinia Ankara-Bavarian Nordic vaccine (MVA-BN) occur within 14 days of receipt of the first dose, according to a research letter published online Sept. 30 in the Journal of the American Medical Association.

Aniruddha Hazra, M.D., from Howard Brown Health in Chicago, and colleagues describe monkeypox infections after a single dose of MVA-BN at a monkeypox testing and vaccination site. Howard Brown Health started performing real-time reverse transcriptase-polymerase chain reaction tests to detect monkeypox in May 2022; MVA-BN was administered to eligible individuals on June 28, 2022. Patients who tested positive for monkeypox after vaccination and through Sept. 9, 2022, were included.

The researchers found that 400 patients tested positive for monkeypox during the study period, and 7,339 individuals received their first dose of MVA-BN. Overall, 90 patients tested positive for monkeypox one day or more after vaccination: 37 and 32 cases occurred at one to seven and eight to 14 days after vaccination, respectively (77 percent of all cases). There was a median of 8.5 days between vaccination and infection. Overall, 36.2 percent of the cases occurring one to 14 days after vaccination were in people with HIV, 96 percent of whom were virologically suppressed. Of the early postvaccination cases without HIV infection, 54 percent were using preexposure prophylaxis. Eight monkeypox cases occurred more than 28 days after the first dose of MVA-BN; 50 percent of the patients had HIV and were virally suppressed.

"These data support public health messaging around behavior modification and risk reduction counseling in the immediate postvaccination period," the authors write.

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