Risk of myocarditis is higher following a SARS-CoV-2 infection than it is following a COVID-19 vaccination and increases significantly in men under 40 years, particularly following a second dose of mRNA-1273 vaccine. The risk is still modest following sequential doses or a booster of BNT162b2 mRNA vaccine. These are among the study findings published in Circulation.
Researchers sought to evaluate risk for myocarditis in younger people following sequential doses of COVID-19 vaccine vs risks of myocarditis in all individuals who develop SARS-CoV-2 infection.
Researchers conducted a self-controlled case series study in England from December 2020 through mid-December 2021 to evaluate if a link exists between COVID-19 vaccination and myocarditis, stratified by age and sex.
They found that among almost 43 million individuals aged at least 13 years, receiving at least 1 dose of vaccine (half receiving 3 doses), there were almost 6 million individuals who developed SARS-CoV-2 infection before or after vaccination. Of these patients, 2861 experienced myocarditis, of which 617 events occurred within 28 days following vaccination.
Risk for myocarditis increased within 28 days following a first dose of ChAdOx1 (incidence rate ratio [IRR], 1.33; 95% CI, 1.09-1.62) and a first dose of BNT162b2 (IRR, 1.52; 95% CI, 1.24-1.85), a second dose (IRR, 1.57; 95% CI, 1.28-1.92), and booster dose of BNT162b2 (IRR, 1.72; 95% CI, 1.33-2.22). This risk was lower than the risk following a positive SARS-CoV-2 test before vaccination (IRR, 11.14; 95% CI, 8.64-14.36) or following vaccination (IRR, 5.97; 95% CI, 4.54-7.87).
Myocarditis risk was greater within 28 days after a second dose of mRNA-1273 (IRR, 11.76; 95% CI, 7.25-19.08) and continued following a booster dose (IRR, 2.64; 95% CI, 1.25-5.58).
Men younger than 40 years faced stronger associations for all vaccines and excess myocarditis events per million people was greater after a second dose of mRNA-1273 than after a positive SARS-CoV-2 test (97; 95% CI, 91-99; vs 16; 95% CI, 12-18). The number of excess events per million among women younger than 40 years was almost identical following a second dose of mRNA-1273 (7; 95% CI, 1-9) vs a positive test (8; 95% CI, 6-8).
“…the risk of myocarditis is greater after SARS-CoV-2 infection than after COVID-19 vaccination and remains modest after sequential doses including a booster dose of BNT162b2 mRNA vaccine,” the study authors wrote.
Patone M, Mei XW, Handunnetthi L, et al. Risk of myocarditis after sequential doses of COVID-19 vaccine and SARS-CoV-2 infection by age and sex. Circulation. Published online August 22, 2022. doi:10.1161/CIRCULATIONAHA.122.059970