The Medical Letter on Drugs and Therapeutics
In Brief: Myocarditis with the Pfizer/BioNTech and Moderna COVID-19 Vaccines (online only)
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Med Lett Drugs Ther. 2021 Jul 26;63(1629):e9
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  • Mark Abramowicz, M.D., President: no disclosure or potential conflict of interest to report
  • Jean-Marie Pflomm, Pharm.D., Editor in Chief: no disclosure or potential conflict of interest to report
  • Brinda M. Shah, Pharm.D., Consulting Editor: no disclosure or potential conflict of interest to report
Upon completion of this activity, the participant will be able to:
  1. Discuss the warning about myocarditis with the Pfizer/BioNTech and Moderna COVID-19 Vaccines.
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On June 25, 2021, the FDA added a warning to the Fact Sheets for the mRNA-based COVID-19 vaccines manufactured by Pfizer/BioNTech (Comirnaty) and Moderna (Spikevax) about an increased risk of myocarditis and pericarditis following administration of the vaccines.1,2

The warning was issued after a review of reports to the Vaccine Adverse Events Reporting System (VAERS) submitted between December 29, 2020 and June 11, 2021 identified 1226 cases of myocarditis following administration of an mRNA vaccine. Cases occurred most commonly in males (76%), in persons <30 years old (58%), and after administration of the second vaccine dose (76%). Symptoms usually developed within a few days after vaccination. At the time of the review, about 296 million doses of mRNA-based COVID-19 vaccines had been administered in the US, including 52 million doses in persons <30 years old.3,4

A CDC analysis of 323 cases of myocarditis following mRNA vaccination in persons 16-29 years old found that 90% of cases were in males and 96% required hospitalization. The median time to symptom onset after vaccination was 2 days. Most cases were mild in severity, and none of the 304 patients with known clinical outcomes died. The CDC estimates that, for every 1 million males 12-29 years old who receive a 2-dose mRNA-based COVID-19 vaccination series, 560 hospitalizations due to COVID-19 would be prevented and 39-47 cases of myocarditis would occur.4

The Advisory Committee on Immunization Practices (ACIP) concluded in a June 23, 2021 meeting that the benefits of mRNA-based COVID-19 vaccination still clearly outweigh the risks for all persons ≥12 years old.5 Adolescents and young adults who experience acute chest pain, shortness of breath, or palpitations after vaccination should be assessed with an ECG, a troponin level, and inflammatory marker testing (e.g., C-reactive protein level, erythrocyte sedimentation rate).6 Myocarditis has not been associated with use of the adenovirus-based Johnson & Johnson (Janssen) COVID-19 vaccine to date.

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