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Acute myocarditis following a third dose of COVID-19 mRNA vaccination in adults

Anthony Simone1, John Herald1, Aiyu Chen2

  • 1Department of Cardiology, Kaiser Permanente Los Angeles Medical Center, Los Angeles, CA, USA.

International Journal of Cardiology
|July 23, 2022
PubMed
Abstract

Insights

COVID-19 mRNA vaccines are associated with a rare risk of myocarditis, particularly after the second dose. The risk of myocarditis after a third dose was not significantly higher than after the second dose.

Area of Science:

  • Cardiology
  • Vaccinology
  • Public Health

Background:

  • Myocarditis cases have been documented following the second dose of COVID-19 mRNA vaccines.
  • The impact of additional vaccine doses on myocarditis risk remains unclear.

Purpose of the Study:

  • To investigate the incidence of myocarditis following first, second, and third doses of COVID-19 mRNA vaccines (BNT162b2 and mRNA-1273).
  • To compare the risk of myocarditis after the third vaccine dose versus the second dose.

Main Methods:

  • Retrospective cohort study of over 3 million individuals receiving 1-3 doses of mRNA COVID-19 vaccines.
  • Myocarditis cases identified within 21 days of vaccination using electronic health records.
  • Incidence rate ratios calculated by comparing observed myocarditis rates to baseline rates.

Main Results:

  • The incidence rate ratio for myocarditis was 0.86 (95% CI 0.31-1.93) for the first dose.
  • The incidence rate ratio for myocarditis was 4.22 (95% CI 2.63-6.53) for the second dose.
  • The incidence rate ratio for myocarditis was 2.61 (95% CI 1.13-5.29) for the third dose, with most cases occurring within seven days of vaccination.

Conclusions:

  • Myocarditis is a rare event following mRNA COVID-19 vaccination, primarily observed after the second and third doses.
  • The incidence of myocarditis after the third dose was not significantly higher than that observed after the second dose.
  • Most myocarditis cases present within seven days of vaccination, suggesting a need for continued surveillance.
Keywords:
Adverse eventBoosterCOVID-19HospitalizationMyocarditisThird-doseVaccination

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