The FDA and CDC are investigating reports that Moderna's COVID-19 vaccine may carry a higher risk of myocarditis — a rare condition that causes inflammation of the heart — than Pfizer's COVID-19 vaccine, two anonymous sources told The Washington Post.
The investigation is focusing on data from Canada that suggests there may be a 2½ times higher incidence of myocarditis in Moderna recipients than in Pfizer recipients, the sources told the Post Aug. 20. They emphasized the risks posed by the vaccines are still probably very uncommon, and COVID-19 poses a much higher risk of heart complications.
The risk of myocarditis after vaccination appears to be greatest for males below the age of 30, the Post reported.
One person familiar with the investigation told the Post it is too early to reach a conclusion about whether Moderna's vaccine carries a higher risk. In June, the FDA added a warning label to both Moderna and Pfizer's shots, saying they carry an increased risk of myocarditis.
FDA spokesperson Stephanie Caccomo told the Post that though the agency won't comment on internal meetings or discussions, "We can say that FDA is absolutely committed to reviewing data as it becomes available to us."
The CDC and its advisory committee on immunization practices told the Post they continue to "review reports of myocarditis and pericarditis following COVID-19 mRNA vaccination. CDC, FDA, and our vaccine safety partners are actively monitoring these reports, including reviewing data and medical records, to learn more and understand any relationship to COVID-19 mRNA vaccination."
The CDC and FDA have confirmed 762 reports of myocarditis and pericarditis following COVID-19 vaccination, out of roughly 202 million Pfizer shots and 142 million Moderna shots administered in the U.S.
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