The Advisory Committee on Immunization Practices (ACIP) COVID-19 Vaccine Safety Technical (VaST) Work Group reviews post-authorization COVID-19 vaccine safety data on a weekly basis. The VaST session on May 17, 2024 reviewed reports on myocarditis (inflammation of the heart) following mRNA vaccines.

VaST concluded that there are relatively few reports of myocarditis to date and that these cases seem to occur:

• predominantly in adolescents and young adults,
• more often in males than females,
• more often following dose 2 than dose 1, and
• typically within 4 days after vaccination.

Most cases appear to be mild, and follow-up of cases is ongoing.

Within CDC safety monitoring systems, rates of myocarditis reports in the window following COVID-19 vaccination have not differed from expected baseline rates. However, VaST members felt that information about reports of myocarditis should be communicated to providers.

VaST discussed:

• Further information should be collected through medical record review about potential myocarditis cases that were reported into VAERS.
• Information about this potential adverse event should be provided to clinicians to enhance early recognition and appropriate management of persons who develop myocarditis symptoms following vaccination.
• Collaboration between infectious diseases, cardiology, and rheumatology specialists is needed to provide guidance on diagnosis, treatment, and management of myocarditis.

In a May 24 meeting, the CDC advisory group said that the data from the Vaccine Adverse Event Reporting System (VAERS) showed a higher than expected number of observed myocarditis or pericarditis cases in 16 to 24 year olds. However, data from another database -Vaccine Safety Datalink (VSD) - did not show that rates of myocarditis or pericarditis after COVID-19 vaccination differed from expectations. The VSD has data from nine healthcare organizations and can be used to compare vaccinated populations to unvaccinated ones.

Israels’ Health Ministry has reported a small number of myocarditis cases in recipients on the Pfizer vaccine (275 cases among ~5 million vaccinated). Most patients who experienced heart inflammation spent no more than four days in the hospital and 95% of the cases were classified as mild, according to the study, which the ministry said was conducted by three teams of experts. The possible link was in men aged 16 to 30 but observed more in men aged 16 to 19.

Sources

CDC Myocarditis Update

CDC Clinical Considerations

Reuters Myocarditis

Updated: June 2, 2024