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Myocarditis Following mRNA Vaccination

 Myocarditis Following mRNA Vaccination
    In May 2021, the U.S. Food and Drug Administration (FDA) expanded Emergency Use Authorization for the Pfizer COVID-19 vaccine to those aged 12-15 years. As vaccines become more available, the percentage of people receiving vaccines are going up: As of June 14, 2021, 52.5% of the U.S. population received at least one vaccine dose. However, since April 2021, there have been increased reports of myocarditis/pericarditis, or inflammation of the heart, after mRNA COVID-19 vaccination (currently, the approved mRNA COVID-19 vaccines in the U.S. are by Pfizer and Moderna). While the reports of myocarditis and pericarditis are rare, the rates for ages 16-24 are higher than expected. On June 10, 2021, the Centers for Disease Control and Prevention (CDC) Vaccines and Related Biological Products Advisory Committee held a meeting where they evaluated cases of myocarditis following vaccination. 

Evaluating the Data

    Data was taken from the Vaccine Adverse Event Reporting System (VAERS), managed by the CDC and FDA. VAERS accepts reports from anyone and analyzes reports of possible health problems. While VAERS can rapidly detect potential safety problems and rare adverse events, its limitation is that it cannot prove that a vaccine caused an event. 

    By May 31, 2021, 789 cases of myocarditis were reported to VAERS after a Pfizer or Moderna vaccine was received. A majority of cases, 573 out of 789, were reported after the second dose of a vaccine. Most cases have been seen in males and the median age for myocarditis after a second dose is 24 years.

    Among the 789 cases of myocarditis, 475 occurred in individuals aged 30 years of younger with the most common symptoms being chest pain, elevated cardiac enzymes, ST or -T wave change, dyspnea or shortness of breath, and then abnormal echocardiography/imaging. The CDC has verified that 226 of these cases meet the working case definition of myocarditis. Out of 280 cases with a known outcome, 270 were discharged. Eighty one percent made a full recovery while the rest had ongoing symptoms or an unknown status. 

    Although individuals under 25 years only make up 8.8% of administered doses, they constitute 52.5% (277 cases) of total reports of myocarditis following a second dose. In teens aged 16-17, 79 cases of myocarditis were observed while the expected number was 2-19 cases. In those aged 18-24 years, 196 cases of myocarditis were observed while the expected number was 8-83 cases. Incidence of myocarditis is clearly higher in younger individuals (under 25 years) than older individuals (25 years and older). 

Going Forward

    After reviewing the data from VAERS, the CDC announced that it "continues to recommend COVID-19 vaccination for everyone 12 years of age and older, given the greater risk of COVID-19 illness and related, possibly severe complications." In other words, the benefits of getting vaccinated outweigh the possible risks, including myocarditis. With only 789 reports of myocarditis out of the 170 million people who have been vaccinated, the risk of developing myocarditis after COVID-19 vaccination is less than one percent. The CDC also emphasizes that most patients with myocarditis who received care responded well and had a quick recovery. In the meantime, the Advisory Committee on Immunization Practices will meet on June 18 to discuss the myocarditis cases. 

Sources

1. Shimabukuro, Tom. “COVID-19 Vaccine Safety Updates.” Vaccines and Related Biological Products Advisory Committee (VRBPAC), Centers for Disease Control and Prevention, 10 June 2021, www.fda.gov/media/150054/download.

2. “Myocarditis and Pericarditis Following MRNA COVID-19 Vaccination.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 27 May 2021, www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/myocarditis.html#print.

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