SILVER SPRING, MD—The U.S. Food and Drug Administration (FDA) has mandated and approved updated warnings on the labeling of Pfizer’s Comirnaty and Moderna’s Spikevax mRNA COVID-19 vaccines to include new safety information regarding the risks of myocarditis and pericarditis.
The updated Prescribing Information for both vaccines now includes details on the estimated incidence of heart inflammation following the 2023-2024 formula of the mRNA COVID-19 vaccines, as well as findings from a study on cardiac magnetic resonance imaging (MRI) in individuals who developed myocarditis post-vaccination.
Specifically, the warning now states that the highest risk of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining outside the heart) has been observed in males aged 12 through 24 years.
Based on analyses of commercial health insurance claims data, the estimated unadjusted incidence of myocarditis and/or pericarditis within seven days of receiving the 2023-2024 Formula mRNA COVID-19 vaccines was approximately 8 cases per million doses for individuals aged 6 months through 64 years. This figure rose to approximately 27 cases per million doses in males aged 12 through 24 years.
The FDA also highlighted results from a longitudinal retrospective observational study that collected follow-up information on cardiovascular outcomes in hospitalized patients diagnosed with COVID-19 vaccine-associated myocarditis. The study found that persistence of abnormal cardiac MRI findings, a marker for myocardial injury, was common at a median follow-up of approximately five months post-vaccination. The long-term clinical significance of these MRI findings is currently unknown.
Information about myocarditis and pericarditis has been included in the vaccine labeling since 2021. The FDA continues to closely monitor the safety of all vaccines, including COVID-19 vaccines, during postmarket use.
A post-approval U.S. study, funded and co-authored by the FDA and published in September 2024, collected follow-up data on approximately 300 individuals who developed myocarditis after receiving the original formula of an mRNA COVID-19 vaccine. Some participants reported persistent heart symptoms approximately three months after their myocarditis diagnosis. Initial and follow-up cardiac MRIs in some individuals commonly showed signs of heart muscle injury, with some improvement over time, but not in all cases. The study noted that it is not yet known if these cardiac MRI findings can predict long-term heart effects of myocarditis.
As part of the approvals for Comirnaty and Spikevax, both manufacturers are required by the FDA to conduct studies to assess potential long-term heart effects in individuals who have experienced myocarditis after receiving an mRNA COVID-19 vaccine. These studies are currently underway.
Suspected adverse events following vaccination can be reported to the Vaccine Adverse Event Reporting System (VAERS), which is jointly managed by the FDA and the Centers for Disease Control and Prevention (CDC).
