Excepts from MedPage Today: Post-Vax Myocarditis Fairly Benign Even in a Diverse Population


MedPage Today

Post-Vax Myocarditis Fairly Benign Even in a Diverse Population

— Experience of California health system suggests cases do not disproportionately affect minorities

by Nicole Lou, Staff Writer, MedPage Today October 4, 2021

A study in a relatively diverse population reaffirmed acute myocarditis as a rare and fairly mild event affecting young men after COVID-19 mRNA vaccination.

There were 15 confirmed cases of myocarditis over a 10-day observation window among the more than 2.3 million Kaiser Permanente Southern California (KPSC) adult members vaccinated against SARS-CoV-2 from December 2020 to July 2021. The two myocarditis cases after a first vaccine dose translated into an incidence of 0.8 cases per 1 million first doses; the 13 cases after a second dose represented 5.8 cases per 1 million second doses.

All 15 individuals were men, with a median age of 25 years, and none had cardiac disease before they were hospitalized for myocarditis. Patients were roughly split between those who had received the Pfizer and Moderna vaccines, reported Ming-Sum Lee, MD, PhD, of Kaiser Permanente Los Angeles Medical Center, and colleagues in JAMA Internal Medicine.

All but one had complained of chest pain in the days immediately after COVID vaccination. All cases of acute myocarditis, independently adjudicated by at least two cardiologists, resolved with conservative management. No one was admitted to the ICU or required readmission after discharge.

Notably, of the people vaccinated in the KPSC system, 37.8% were Hispanic, 31.2% were white, 14.3% were Asian, and 6.7% were Black. Women accounted for 54.0% of the total cohort, and median age was 49 years (35.7% of individuals were younger than 40 years). Of the 15 men who developed myocarditis, nine were white, four were Hispanic, one was Asian, and one was of unknown ethnicity.

“This is an important study since it further provides evidence for a rare but clinically important adverse event with mRNA vaccination. The diverse population helps generalize the data to the larger population,” wrote Amanda Verma, MD, and Kory Lavine, MD, PhD, both of Washington University School of Medicine in St. Louis, in a joint commentary provided to MedPage Today.

The incidence rate ratio (IRR) for myocarditis was found to be statistically no greater after the first dose of COVID vaccination than for unexposed individuals during the study period; it was the second dose that put vaccinated individuals over the edge in excess risk (IRR 2.7, 95% CI 1.4-4.8), Lee and colleagues noted.

These findings were consistent with sensitivity analyses using vaccinated people as their own controls based on the incidence of myocarditis during a 10-day period a year prior to vaccination.

Bozkurt concluded that the KPSC report supports prior studies suggesting a small risk for myocarditis after mRNA vaccination, predominantly in young men.

Moreover, the risk of post-vaccination myocarditis is “small when weighed with the morbidity and mortality of COVID-19 infection, in which up to 28% of hospitalized patients showed signs of myocardial injury,” according to an accompanying editorial by two members of the JAMA Internal Medicine team.

“No relationship between COVID-19 mRNA vaccination and postvaccination myocarditis can [be] established given the observational nature of this study,” they cautioned.

“Nonetheless, studies such as this one continue to observe a fortunately rare but clinically significant adverse effect of COVID-19 mRNA vaccines that is important for the medical community to recognize,” wrote Verma and Lavine.

  • Nicole Lou is a reporter for MedPage Today, where she covers cardiology news and other developments in medicine. Follow 


The study authors and editorialists reported no relevant disclosures.

Bozkurt, Verma, and Lavine reported no disclosures.

Primary Source

JAMA Internal Medicine

Source Reference: Simone A, et al “Acute myocarditis following COVID-19 mRNA vaccination in adults aged 18 years or older” JAMA Intern Med 2021; DOI: 10.1001/jamainternmed.2021.5511.

Secondary Source

JAMA Internal Medicine

Source Reference: Guduguntla V, Katz MH “COVID-19 messenger RNA vaccination and myocarditis — a rare and mostly mild adverse effect” JAMA Intern Med 2021; DOI: 10.1001/jamainternmed.2021.5634.


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