COVID-19 mRNA vaccination and myocarditis or pericarditis

Published: June 11

In April, 2021, international news media first reported rare cases of young men in Israel who had developed myocarditis shortly after vaccination with the Pfizer-BioNTech mRNA vaccine against SARS-CoV-2.1 Since then, many observational studies from Asia,2 Europe,345 the Middle East,67 and North America89 have found COVID-19 mRNA vaccination to be associated with a short-term increased risk of myocarditis. Furthermore, this association has been established using multiple types of analysis, including comparisons of observed-to-expected rates,689 case-control studies,2 self-controlled cases series,34 and cohort studies.457In The Lancet, Hui-Lee Wong and colleagues10 robustly replicate the previous findings using large-scale US health plan claims data. Notably, the new study uses data from four health plan databases, covering more than 100 million individuals. Of these, 15 148 369 were aged 18–64 years and registered to have received a COVID-19 mRNA vaccine (53·1% male and 13·0% aged 18–25 years).

Similar to previous studies, Wong and colleagues10 observed higher than expected rates of myocarditis (and pericarditis, a closely related clinical presentation), specifically in individuals younger than 35 years, with the highest risk among men aged 18–25 years after their second COVID-19 mRNA vaccine dose. The absolute risk of myocarditis or pericarditis, calculated as the incidence rate within 1–7 days of vaccination, for men aged 18–25 years after a second vaccination dose was 2·17 (95% CI 1·55–3·04) cases per 100 000 person-days for the Moderna vaccine, mRNA-1273, and 1·71 (1·31–2·23) cases per 100 000 person-days for the Pfizer-BioNTech vaccine, BNT162b2. Furthermore, the study supports the previous finding that the association is principally short term. The data indicate that this adverse event primarily occurs within 1–7 days of vaccination, because a longer duration of follow-up attenuated the association. Although not significantly different, the study found a tendency towards a higher risk of myocarditis after vaccination with mRNA-1273 in a head-to-head comparison with BNT162b2 (with an adjusted incidence rate ratio of 1·43 [95% CI 0·88–2·34] among men aged 18–25 years). Similar findings of a more pronounced risk of myocarditis after mRNA-1273 in comparison with BNT162b2 have been observed in other large observational studies.3–5,9

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