Two recent reports in JAMA Cardiology describe 30 patients with myocarditis, or inflamed heart muscles, less than a week after receiving either a Pfizer/BioNTech or Moderna mRNA COVID-19 vaccine.
While these events may indicate a higher prevalence of myocarditis than expected, both reports note their rarity.The researchers of the larger report, which described myocarditis in 23 US military men, noted that in the same period, the US Military Health System vaccinated more than 2.8 million people with mRNA-based COVID-19 vaccines.
For the second study, the four identified cases of myocarditis at Duke University Medical Center were among more than 560,000 people estimated to have received two doses of an mRNA vaccine in the six surrounding