Risk of myocarditis due to COVID-19 vaccination far less than COVID-19 infection

30 Dec 2021

Post vaccination myocarditis has been reported as a rare side effect, but mostly seen in young adults and adolescent males, after the vaccination of COVID-19 messenger ribonucleic acid (mRNA) vaccines.1 Myocarditis was historically defined as rare adverse event after vaccinations like smallpox vaccination, influenza, hepatitis B or other vaccinations.2 The overall rate of myocarditis in the general population was approximately limited to 10 to 20 individuals per 100,000 per year, with 0.1% of 620,195 reports filed at the Vaccine Adverse Event Reporting System between 1990 and 2018 had myocarditis, and 79% of them were males.2 The mechanisms implicated for COVID-19 mRNA vaccines related myocarditis included molecular mimicry between spike protein and self-antigens, dysregulated immune response, auto-antibody production against cardiac proteins, immunogenicity of RNA in certain individuals, and testosterone.2

A rare incidence of 148 myocarditis cases in 10.4 million vaccinated individuals, mostly amongst males aged 16 to 30 years, within 30 days of second dose of COVID-19 mRNA vaccination was initially reported from Israeli Ministry of Health, with a prevalence of 1/20,000 for the 16- to 30-year age group compared with 1/100,000 in the general population receiving the same vaccine.2 Most individuals hospitalized had mild symptoms which resolved without treatment.2 Similarly, the United States Department of Defense also reported a low incidence of myocarditis amongst military personnel mostly after the second dose of COVID-19 mRNA vaccination, with 23 myocarditis cases in 2.8 million vaccinated individuals equating to a prevalence of 1/100,000 cases.2

Professor Biykem Bozkurt from the Baylor College of Medicine observed that a majority of young males presented with chest pain, electrocardiogram (ECG) abnormality, cardiac troponin elevation, and CMR abnormality within 2-3 days after the second dose of COVID-19 mRNA vaccination.2 Some preceded with fever and myalgia a day after vaccination, and need hospitalization for myocarditis, but symptoms resolved without treatment.2 Most of the reported cases had no prior history of COVID-19 or comorbidities and tested negative for current COVID-19 infection or other virus antibodies, with a spike in SARS-CoV-2 antibody levels showing the vaccination was effective.2

Findings from the Centers for Disease Control and Prevention (CDC) reflected the crude reporting rate of myocarditis was highest amongst males aged 12-17 years, with a prevalence of approximately 7 in 100,000 COVID-19 mRNA vaccination cases. After a systemic review on those cases, CDC reassured that the benefits of COVID-19 mRNA vaccination outweigh the risks, such as hospitalization, intensive care unit (ICU) admission and death, and the cardiovascular complications associated with COVID-19 infection including deep vein thrombosis, myocardial infection, and pulmonary embolism, in all the populations including young adolescents and young adults.2

The active surveillance data of all the myocarditis cases from Israel also confirmed that incidence of myocarditis following COVID-19 mRNA vaccination was quite low amongst the general population and individuals aged between 16 to 29 years.2 The safety data from the clinical trials of COVID-19 mRNA vaccination already confirmed that the vaccination is safe for children aged 5-11 years, and the most common side effects were just pain at the injection site and did not include myocarditis.2 Prof. Bozkurt emphasized that clinicians need to be aware of the risks and benefits of COVID-19 mRNA vaccination, with data supporting the low risk of myocarditis post vaccination and all symptoms are mild which can resolve in 4-5 days, COVID-19 mRNA vaccination should be encouraged in all populations.1

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