Although the risk for myocarditis or myopericarditis was significantly increased in individuals aged 12 to 39 years who received the mRNA-1273 (Moderna) COVID-19 vaccine, the BNT162b2 (Pfizer-BioNTech) vaccine significantly increased the risk for both diseases among only women,, according to results of a study published in BMJ.

Researchers performed a population-based cohort study that included a total of 4,931,775 participants aged 12 years and older who were followed from October 2020 to October 2021. The researchers sought to assess the association between SARS-CoV-2 vaccination and the risk for myocarditis or myopericarditis. The primary outcome was myocarditis and myopericarditis, defined as a combination of a hospital diagnosis of myocarditis or pericarditis, increased troponin concentrations, and hospitalization lasting more than 24 hours. In addition, prevaccination follow-up time was compared with postvaccination follow-up time between days 0 and 28 from the day of vaccination for both the first and second doses.

Among a total of 3,482, 295 participants who received the BNT162b2 vaccine, 48 developed myocarditis or myopericarditis within 28 days (adjusted hazard ratio [aHR], 1.34; 95% CI, 0.90-2.00). After stratification by participant sex, the researchers noted that the aHR among women and men was 3.73 (95% CI, 1.82-7.65) and 0.82 (95% CI, 0.50-1.34), respectively. In participants aged 12 to 39 years, the aHR was 1.48 (95% CI, 0.74-2.98).

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Among a total of 498,814 participants who received the mRNA-1273 vaccine, 21 developed myocarditis or myopericarditis within 28 days (aHR, 3.92; 95% CI, 2.30-6.68). After stratification by participant sex, the aHR among women and men was 6.33 (95% CI, 2.11-18.96) and 3.22 (95% CI, 1.75-5.93), respectively. In participants aged 12 to 39 years, the aHR was 5.24 (95% CI, 2.47-11.12) within 28 days of vaccination.

Although neither the first nor second dose of the BNT162b2 vaccine was found to increase the risk for myocarditis or myopericarditis, the second dose of the mRNA-1273 vaccine was associated with an increased risk for both diseases.

Study limitations included the potential for selection, detection, and surveillance bias due to the observational design, and the potential for confounding due to recent exposure to SARS-CoV-2.

According to the researchers, “…the clinical outcomes [of participants who developed] myocarditis or myopericarditis were predominantly mild, providing evidence to support the overall safety of SARS-CoV-2 mRNA vaccines.” They concluded that “…larger multinational studies and meta-analyses are needed to specify risks within smaller subgroups and the risk [for] myocarditis or myopericarditis after SARS-CoV-2 infection vs vaccination.”

Disclosure: Some authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.   


Husby A, Vinsløv Hansen J, Fosbøl E, et al. SARS-CoV-2 vaccination and myocarditis or myopericarditis: population based cohort study. BMJ. 2021;375:e068665. doi:10.1136/bmj-2021-068665

This article originally appeared on Infectious Disease Advisor