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 counties.
"People of all ages should choose to get a COVID-19 vaccine because the risks are extremely low compared to the benefits. Additionally, the growing body of research shows that vaccine-associated myocarditis resolves quickly in almost all cases," said Leslie T. Cooper Jr., MD, senior author of the military study, in a Mayo Clinic press release.
Quick symptom onset, uncomplicated recovery
The 23 US military men (median age, 25) all received mRNA-based COVID-19 vaccines from Jan 1 to Apr 30, with 16 receiving Moderna and 7 receiving Pfizer 4 days prior to symptom onset. All had severe chest pain as well as 10- to 400-fold increased cardiac troponin levels, which indicates heart damage. Three had been infected with COVID-19 prior to vaccination and had symptoms after their first dose, while the rest had symptoms after their second. None of the patients had findings consistent with infectious, ischemic, or autoimmune etiologies.
As of the time of writing, 16 patients' symptoms resolved within 1 week, while the rest still have some chest discomfort.
"The observed number of male military members who experienced myocarditis after their second dose of mRNA vaccine, while relatively small, is substantially higher than the expected number," the researchers note. Because of the pandemic and the overall benefits, though, they still advocate for use of the Pfizer and Moderna vaccines.
Of the patients treated at Duke University Medical Center from Feb 1 to Apr 30, three were men ages 23 to 36 and one was a 70-year-old woman diagnosed as having atherosclerosis shortly after admission. Half received the Moderna vaccine, and half received the Pfizer vaccine 1 to 5 days prior to hospitalization. No one had a history of COVID-19.
All four presented with severe acute chest pain, abnormal electrocardiograms, and increased troponin. After 2 to 4 days of conservative treatment (with one person receiving corticosteroids), everyone made a full recovery.
The researchers say further study is needed to know whether patients who experience myocarditis post-vaccination should receive potential COVID-19 boosters and if myocarditis is associated with non-mRNA COVID-19 vaccines.
The importance of vaccine surveillance
While myocarditis has not been officially listed as a rare adverse event related to mRNA-based COVID-19 vaccines, an editorial related to both reports lines up the circumstantial evidence. "The striking clinical similarities in the presentations of these patients, their recent vaccination with an mRNA-based COVID-19 vaccine, and the lack of any alternative etiologies for acute myocarditis suggest an association with immunization," write David Shay, MD, MPH, of the US Centers for Disease Control and Prevention, and colleagues.
They continue, "Myocarditis or pericarditis were not detected in the clinical trials for these vaccines; however, it is possible that any association is too rare for recognition in a clinical trial enrolling less than several hundred thousand participants."
A separate editorial takes a different angle, focusing not on the likelihood of myocarditis but on the importance (and current success) of the vaccine safety surveillance system.
"Prior reports of adverse events following immunization for measles, mumps, and rubella, later deemed unsubstantiated, raised significant public alarm and led to vaccine resistance—an effect that lingers to this day," write Ann Marie Navar, MD, PhD, of UT Southwestern Medical Center in Dallas, and colleagues.
"This temporal association [with mRNA-based COVID vaccines] does not establish causality, especially because a myocarditis-like syndrome has been seen following SARS-CoV-2 infection," the authors write. "Rather, these case series highlight the need for additional surveillance and investigation."