New Research on Clinical Course of Vaccine-Associated Myocarditis Helps Clarify Risk, Characterize Syndrome in Adolescents and Young Adults

Vaccine-associated myocarditis (VAM) is a rare, but real side effect of COVID-19 mRNA vaccination, presenting disproportionately in younger adult males and adolescents in days to a week or two  after administration of a second dose. The U.S. Centers for Disease Control and Prevention (CDC) currently estimates a VAM incidence of between 10 and 70 cases per million for younger males, based on reporting from multiple countries and U.S. jurisdictions; the rate for young women and adolescent girls is substantially lower. Early Israeli data on mRNA vaccinations for children under the age of twelve years and booster shots in the adolescent population suggest the same or lower rates of VAM in these populations.

The U.S. Food and Drug Administration (FDA), CDC, and relevant medical specialty societies, including the American Academy of Pediatrics and the ACC, all conclude that the benefits of pediatric, adolescent, and young adult mRNA vaccination against COVID-19 consistently and materially outweighs the risk of harm, particularly in preventing severe COVID-19, hospitalization, and multi-inflammatory syndrome-children (MIS-C), although individual patient risk-benefit should be considered in unique circumstances.

While the epidemiology on the risk-benefit of mRNA vaccination for younger patients is clear, reporting in the medical literature on the clinical course of VAM has been largely limited to individual case reports or generalized findings from generic vaccine surveillance systems with limited follow-up. Truong, et al., make a significant contribution to the understanding of the natural history of VAM in their recent research article, summarizing the clinical course 139 patients with myocarditis diagnosed using standardized criteria within 30 days of mRNA vaccination in patients under 21 years.

In general, Truong, et al., conclude the majority of adolescents and young adults with suspected VAM experience a very mild clinical course with rapid recovery from symptoms. Nonetheless, they provide information for the small subset that has more concerning episodes of VAM. Although elevated troponin, electrocardiographic changes, and cMRI findings indicative of myocardial injury are common, most patients exhibit normal ventricular systolic function on echocardiogram. There were no fatalities among the 139 patients studied. Among those hospitalized, median length of stay was two days, 19% required care in the intensive care unit (ICU) care and 1% required vasoactive/inotropic medications; none had sustained ventricular arrhythmias.

The authors stress the need for continued research to better understand the underlying biological mechanism of the VAM syndrome, identify predictors of VAM risk, and clarify the optimal clinical approach. The article succinctly summarizes current hypotheses on the underlying mechanism, identifies various approaches to clinical management, and details several cases of particularly interesting clinical presentation.



Truong DT, Dionne A, Muniz JC, et al. Clinically suspected myocarditis temporally related to COVID-19 vaccination in adolescents and young adults. Circulation 2021;Dec. 6:[Epub ahead of print].

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Clinical Topics: Arrhythmias and Clinical EP, COVID-19 Hub, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias

Keywords: Troponin, Pediatrics, Arrhythmias, Cardiac, Vaccination, Centers for Disease Control and Prevention, U.S., RNA, Messenger, Myocarditis, COVID-19

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