1. The highest incidence of myocarditis or pericarditis was seen after the second dose of Moderna (mRNA-1273) in young men aged 18-25 years (2.17 per 100 000 person-days).

2. Although no statistically significant difference in incidence of myocarditis or pericarditis was seen between the BNT172b2 and mRNA-1273 vaccines, a difference should not be ruled out.

Evidence Rating Level: 2 (Good)

Study Rundown: Passive surveillance programs have identified a potential risk of myocarditis or pericarditis following COVID-19 mRNA vaccination. This study retrospectively analyzed individual patient health data from four databases in the USA. Overall, among 15 148 369 individuals vaccinated with at least one dose, 411 events of myocarditis or pericarditis were identified within seven days post-vaccination. The highest number of events was seen in young men aged 18-25 years old after the second dose. There was no statistically significant difference seen between the two different mRNA vaccines from Pfizer and Moderna. Limitations to this study include the limited data that is available based on claims information other than age and sex. Nevertheless, this study is consistent with existing surveillance reports indicating an increased incidence of myocarditis and pericarditis following COVID-19 mRNA vaccination. This study supports the continued use of mRNA vaccines for immunization against COVID-19 infection given the low incidence of myocarditis and pericarditis seen and favorable benefit-to-risk profile.

Click to read the study in the Lancet

Relevant Reading: Myocarditis after BNT162b2 mRNA Vaccine against Covid-19 in Israel

In-Depth [retrospective cohort study]: Data for this retrospective cohort study was collected from four databases (Optum, HealthCore, Blue Health Intelligence, and CVS Health). Eligibility criteria included individuals aged 18-64 years old who had received at least one dose of a COVID-19 mRNA vaccine. Exclusion criteria included myocarditis, pericarditis or both 365 days prior to vaccination. A total of 15 148 369 eligible individuals were identified with 12-14% aged 18-25 years old and 52-53% were men. There were 411 post-vaccination myocarditis or pericarditis events recorded. In comparison to vaccinees, 33-42% of myocarditis and pericarditis events occurred in people aged 18-25 years old and 58-73% were male. Among men aged 18-25 years, the incidence rate after the second dose was 1.71 per 100 000 person-days for BNT162b2 and 2.17 per 100 000 person-days for mRNA-1273. Comparing the incidence between the two mRNA vaccines demonstrated an IRR of 1.43 (95% CI 0.88 to 2.34) with mRNA-1273 compared to BNT162b2, but this was not statistically significant.

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