By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

SYNOPSIS: The occurrence of myocarditis after receipt of COVID-19 mRNA vaccines is most frequent in young males and generally is benign, with rapid resolution with only supportive care. Careful analysis indicates that the benefit of vaccination outweighs the risk in all groups for whom the vaccine is recommended — including young males.

SOURCE: Gargano JW, Wallace M, Hadler SC, et al. Use of mRNA COVID-19 vaccine after reports of myocarditis among vaccine recipients: Update from the Advisory Committee on Immunization Practices — United States, June 2021. MMWR Morb Mortal Wkly Rep 2021;70:977-982.

From December 2020, when the Food and Drug Administration (FDA) issued Emergency Use Authorization for the use of Moderna and Pfizer-BioNTech mRNA COVID-19 vaccines, through June 11, 2021, approximately 296 million doses were administered in the United States, including 52 million doses given to individuals 12-29 years of age. Within that interval, beginning Dec. 29, 1,226 reports of post-vaccination myocarditis were reported to the Vaccine Adverse Event Reporting System (VAERS). The median age of those reported was 26 years (range, 12-94 years), with a median onset three days after vaccination. The majority were 30 years of age, and most of this younger group were male.

A further review of 323 patients who met Centers for Disease Control and Prevention (CDC) definitions for myocarditis, pericarditis, or myopericarditis was performed. All but 4% of these were hospitalized. The median age was 19 years, and 291 of the 323 were male. The median interval between vaccination and onset was two days (range, 0-40 days), with 92% having onset within seven days. The clinical course was mild, with no deaths and with 95% discharged from the hospital at the time of review.

For males 12-29 years of age, the myocarditis reporting rate occurring within seven days of a second vaccine dose was 40.6 per million, while it was 2.4 per million for males > 30 years of age. The rates for women in these age groups were 4.2 and 1.0 per million, respectively. The groups with the highest rates were males 12-17 years of age (62.8 per million) and males 18-24 years of age (50.5 per million).

Analysis led to the conclusion that the benefits associated with the prevention of COVID-19 outweighed the risk of myocarditis in all groups for whom vaccination has been recommended. Focusing on males 12-29 years of age, receiving both vaccine doses was associated with 39-47 cases of myocarditis but with prevention of 11,000 COVID-19 cases, 560 hospitalizations, 138 intensive care unit (ICU) admissions, and six deaths. It also should be noted that this analysis did not take into account the prevention of “long COVID.”


Numerous case reports and small case series describing myocarditis after COVID-19 mRNA vaccination are appearing in the literature, and these attest to the usual apparent benign nature of this complication. As one example, Marshall and colleagues reported seven cases in adolescents. All had elevated cardiac troponin levels, and all had late enhancement of magnetic resonance imaging (MRI) images with gadolinium enhancement, a characteristic finding in myocarditis.1 All patients recovered rapidly without apparent sequelae.

Montgomery et al described 23 cases of myocarditis identified within the U.S. Military Health System that occurred over a period during which more than 2.8 million mRNA vaccine doses had been administered.2 All were male and their median age was 25 years (range, 20-51 years). All had elevated serum troponin, and MRI findings were consistent with myocarditis in all eight patients in whom this study was performed. Their illnesses were mild, and all had recovered or were recovering at the time the report was submitted for publication.

The benign nature of the illness described in these series is consistent with the CDC report and conclusions. As they indicate, it will be important that follow-up of these cases continues to assure the absence of any longer-term adverse effects. 


  1. Marshall M, Ferguson ID, Lewis P, et al. Symptomatic acute myocarditis in seven adolescents following Pfizer-BioNTech COVID-19 vaccination. Pediatrics 2021; Jun 4:e2021052478. doi: 10.1542/peds.2021-052478. [Online ahead of print].
  2. Montgomery J, Ryan M, Engler R, et al. Myocarditis following immunization with mRNA COVID-19 vaccines in members of the US military. JAMA Cardiol 2021; Jun 29. doi: 10.1001/jamacardio.2021.2833. [Online ahead of print].