In a recent publication in Clinical Infectious Diseases, researchers report that myocarditis occurred more among adult men who received an mRNA-based COVID-19 vaccination than among the general population. The scientists conducted a retrospective case series using the Mayo Clinic COVID-19 Vaccine Registry. The researchers measured the incidence rate ratio for myocarditis temporally related to COVID-19 mRNA vaccination compared with myocarditis in a comparable population from 2016 through 2020. Clinical characteristics and outcomes of the affected patients were collected, and 21 individuals were identified, but ultimately seven patients met the inclusion criteria for vaccine-associated myocarditis.

The seven patients with possible vaccine-related myocarditis had an average age of 44 years (range, 22-71 years), six were men, and all were Caucasian. The most common comorbidities in subjects were hypertension (n = 5), obesity (n = 4), obstructive sleep apnea (n = 4), dyslipidemia (n = 3), tobacco use (n = 3), history of myocarditis (n = 1), and previous SARS-CoV-2 infection (n = 1). The vaccines received were either Moderna (n = 4) or Pfizer-BioNTech (n = 3).

The researchers indicated that myocarditis was diagnosed between 1 and 13 days after vaccination, and six study participants developed myocarditis after receiving the second dose. During electrocardiogram, five had ST-segment changes, and three patients were evaluated for acute coronary syndrome due to elevated troponin T-levels. Cardiac catheterization and computed tomography examination discovered normal arteries for two and one patient(s), respectively. During echocardiogram, three patients had reduced left ventricular ejection fraction and right ventricular dysfunction. A magnetic resonance imaging scan found delayed enhancement among six patients and pericardial involvement among three patients.

The researchers also noted that overall cases of myocarditis were mild, and patients were treated with colchicine (n = 5), steroids (n = 2), nonsteroidal anti-inflammatory drugs (n = 2), angiotensin-converting enzyme inhibitors (n = 3), and beta-blockers (n = 3), and there were no reported deaths.

The authors concluded that myocarditis is a rare adverse event associated with COVID-19 mRNA vaccines and occurs in adult males with significantly higher incidence than in the background population. They also note that recurrence of myocarditis after a subsequent mRNA vaccine dose is not known at this time.

The authors wrote, "Patients with preexisting cardiovascular disease or prior history of myocarditis may be at increased risk for COVID-19 vaccine–related myocarditis, but more data are needed. The condition is more often seen after the second dose of the COVID-19 mRNA vaccine. Post-immunization myocarditis is relatively straightforward to diagnose and treat, and the clinical course tends to be mild in most patients. As COVID-19 vaccination continues and expands to younger populations, physicians should remain vigilant and report suspected vaccine adverse events to the CDC through the Vaccine Adverse Event Reporting System, which has detected safety signals for this and other vaccine-associated adverse events. Despite the increased frequency of this rare condition following COVID-19 vaccination, the benefits of COVID-19 vaccination far exceed the risk, and vaccination is strongly recommended by the authors. Vaccination is an effective means to prevent COVID-19 infection, transmission, and related complications."

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