How common is myocarditis after an mRNA booster?

Embargoed until: Publicly released: 2022-03-18 11:30

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Myocarditis, inflammation of the heart muscle that can be a rare side effect of mRNA vaccines, remains rare after a third dose in young people, according to an Israeli study. The team looked at myocarditis rates among a group of about 125,000 members of the Israeli Defence Force who received Pfizer as a booster. The majority of participants were aged 18-24, with previous studies showing men in that age bracket to be at a relatively higher risk than older male booster recipients and women. Nine participants, all young men, were diagnosed with myocarditis during the study, including one man who was excluded from the results because the condition occurred after a COVID-19 infection. The researchers estimate the incidence rate of myocarditis in the two weeks following a booster is 5.55 per 100,000. In young men specifically, they say the rate is 11.25 per 100,000. All myocarditis cases in the study were mild with no ongoing injury after hospital discharge.