A retrospective case-series study found that although a rare adverse event, myocarditis occurred more among adult men who received an mRNA-based COVID-19 vaccination than among the background population. The findings were published in Clinical Infectious Diseases.
For the study, researchers sourced data from the Mayo Clinic COVID-19 Vaccine Registry. The database was queried for diagnoses of myocarditis following a vaccination with an mRNA-based COVID-19 product from December 17, 2020 through May 13, 2021. As a comparator group, the incidence rate of myocarditis was assessed among the general population from data in the Rochester Epidemiology Project (REP) collected between 2016 and 2020.
At the time of analysis, there were data from 175,472 individuals, including 718 adolescents aged 12-15 years in the Vaccine Registry.
Myocarditis occurred among 21 individuals after vaccination. After further analysis, 14 of these cases appeared not to be vaccine related.
The 7 patients with possible vaccine-related myocarditis had a median age of 44 (range, 22-71) years, 6 were men, and all were White. The most common comorbidities were hypertension (n=5), obesity (n=4), obstructive sleep apnea (n=4), dyslipidemia (n=3), tobacco use (n=3), a history of myocarditis (n=1), and a previous SARS-CoV-2 infection (n=1).
The vaccines received were either Moderna (n=4) or Pfizer-BioNTech (n=3).
Myocarditis was diagnosed between 1 and 13 days after vaccination, and 6 study participants developed myocarditis after receiving the second dose.
During electrocardiogram, 5 had ST-segment changes and 3 patients were evaluated for acute coronary syndrome due to elevated troponin T-levels. Cardiac catheterization and computed tomography examination found normal arteries for 2 and 1 patient(s), respectively. During echocardiogram, 3 patients had reduced left ventricular ejection fraction and right ventricular dysfunction. A magnetic resonance imaging scan found delayed enhancement among 6 patients and pericardial involvement among 3.
Overall cases were mild, and patients were given colchicine (n=5), steroids (n=2), nonsteroidal anti-inflammatory drugs (n=2), angiotensin-converting enzyme inhibitors (n=3), and beta-blockers (n=3). No deaths occurred.
The incident rate of myocarditis among the vaccination registry was 55.35 (95% CI, 22.25-114.00) per 100,000 person-years (py) compared with 13.25 (95% CI, 10.60-16.36) among the general population. Stratified by gender, the incident rate ratio (IRR) was 6.69 (95% CI, 2.35-15.52) for men and 1.41 (95% CI, 0.03-8.45) for women.
This study was limited by the lack of racial and ethnic diversity among the registry participants, so these findings may not be generalizable to other populations.
The study data suggested that the rare adverse event to an mRNA-based COVID-19 vaccine, myocarditis, occurred at a higher rate than the background population among adult men.
“Patients with pre-existing cardiovascular disease or prior history of myocarditis may be at increased risk for COVID-19 vaccine-related myocarditis, but more data are needed,” the study authors said. “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.”
Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.
Perez Y, Levy ER, Joshi AY, et al. Myocarditis following COVID-19 mRNA vaccine: a case series and incidence rate determination. Clin Infect Dis. 2021;ciab926. doi:10.1093/cid/ciab926