A new study of 23.1 million Scandinavians suggests that the risk of myocarditis after mRNA COVID-19 vaccination is low but highest in 16- to 24-year-old males after the second dose. The results were published yesterday in JAMA Cardiology.

Researchers from the Norwegian Institute of Public Health studied the incidence of myocarditis (inflammation of the heart muscle) and pericarditis (swelling of the tissues around the heart) among residents of Denmark, Finland, Norway, and Sweden aged 12 and older before vaccination or 28 days after the first or second vaccine doses.

Eighty-one percent of participants were vaccinated by study end. All were followed from Dec 27, 2020, to Oct 5, 2021.