BACKGROUND AND PURPOSE:

• There have been reports of myocarditis and pericarditis in mRNA COVID-19 vaccine recipients, primarily among young males receiving their second dose
• Gargano et al. (CDC MMWR, 2021) report on the incidence of myocarditis following mRNA vaccination, and assessed the benefit-risk balance of mRNA vaccines in adolescents and young adults

METHODS:

• Population
  • Within the Vaccine Adverse Event Reporting System (VAERS)
    • Individuals administered an mRNA-based COVID-19 vaccine in the U.S.
  • In CDC rapid review of myocarditis
    • A subset of individuals aged <30 years who met CDC’s case definitions for myocarditis
• Study design
  • To assess the benefit-risk balance of mRNA vaccines in adolescents and young adults, an individual-level assessment compared benefits (i.e., COVID-19 infections and severe disease prevented) to risks (number of cases of myocarditis)
    • Analysis assumed 95% vaccine effectiveness and assessed outcomes for a 120-day period

RESULTS:

• 296 million doses of mRNA COVID-19 vaccines administered as of June, 2021
  • 52 million doses administered to persons aged 12 to 29 years
• Reports of myocarditis after vaccination between December 29, 2020 and June 11, 2021 in VAERS: 1,226 reports
  • Median age: 26 years (range 12 to 94 years)
  • Median symptom onset: 3 days after vaccination (range 0 to 179 days)
  • Among 1212 cases of myocarditis with sex reported
    • Male: 923 cases
    • Female: 289 cases
  • Among 1094 cases of myocarditis with number of vaccine doses reported
    • After dose 1: 24%
    • After dose 2: 76%
• Myocarditis in CDC review: 323 cases
  • Median age: 19 years (range 12 to 29 years)
  • The median symptom onset: 2 days (range 0 to 40 days)
    • 92% experienced onset with 7 days of vaccination
  • Sex reporting ratio
    • Male: 291 cases
    • Female: 32 cases
  • Hospitalizations: 96%
    • Acute clinical courses were generally mild
    • Discharges among hospitalized patients: 95%
    • No deaths
• Myocarditis reporting rates in VAERS
  • Males
    • Aged 12 to 29 years: 40.6 cases per million second doses
    • Aged ≥30 years: 2.4 per million second doses
  • Females
    • Aged 12 to 29 years: 4.2 cases per million second doses
    • Aged ≥30 years: 1.0 per million second doses
• The benefits of vaccination outweighed the risks in all populations for which vaccination has been recommended
  • Per million second doses of mRNA COVID-19 vaccine administered to males aged 12 to 29 years
    • Benefits: 11,000 COVID-19 cases, 560 hospitalizations, 138 ICU admissions, and six deaths due to COVID-19 prevented
    • Risks: 39 to 47 expected myocarditis cases
  • Among males aged ≥30 years
    • Benefits: 15,300 COVID-19 cases, 4,598 hospitalizations, 1,242 ICU admissions, and 700 deaths prevented
    • Risks: 3 to 4 expected myocarditis cases

CONCLUSION:

• Myocarditis is a rare complication of mRNA-based COVID-19 vaccination, with 1,226 reports in the US, out of 296 million doses administered
• Myocarditis is more common in males under the age of 30 receiving their second dose,
  • Cases in this population remain rare, with a reporting rate of 40.6 cases per million second doses
• The clinical course of myocarditis cases is generally mild
  • No deaths have been reported
• The Advisory Committee on Immunization Practices (ACIP) has concluded that the benefits of vaccination outweigh risks regarding myocarditis in all populations in which vaccination has been recommended

Learn More – Primary Sources:

Use of mRNA COVID-19 Vaccine After Reports of Myocarditis Among Vaccine Recipients: Update from the Advisory Committee on Immunization Practices — United States, June 2021

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