COVID-19 Myocarditis in Children

Myocarditis is uncommon in children but occurs more commonly among those with COVID-19. In a recent study published in the Morbidity and Mortality Weekly Report from the Centers for Disease Control (CDC), only 86 children <16 years of age were diagnosed with myocarditis among nearly 65,000 (0.133%) children with COVID-19. During the same time period (March 2020-January 2021), 132 out of nearly 4 million children without COVID-19 developed myocarditis. Although the overall risk was low, the data translate to a risk of myocarditis that is more than 30 times higher among COVID-19 patients. The study reviewed health encounters of more than 900 US hospitals and excluded any patients who had received a COVID-19 vaccine. The methods used for making a diagnosis of myocarditis were not described.

The study also found that COVID-19 patients <16 years of age had a risk of myocarditis similar to that of patients >75 years of age but much greater than all other age groups. In addition, the risk difference for myocarditis was increased in males compared to females. The numbers of cases of COVID-19 myocarditis spiked in April 2020 and again during the COVID-19 surge of December 2020.

The study investigators speculate that the diagnosis of myocarditis among patients <16 years of age may represent cases of the multisystem inflammatory syndrome in children (MIS- C). MIS-C is a clinical syndrome that usually occurs 2-4 weeks after infection with the SARS- CoV-2 coronavirus. It usually manifests with fever, rash, swollen lymph glands and conjunctivitis. In some patients cardiovascular complications are seen including shock, coronary artery dilation and depressed ventricular function. Fortunately, most children who develop MIS-C will recover without chronic cardiac disease.

When SARS-CoV-2 virus infects the muscle cells of the heart, it begins to replicate and damage the cell. The body’s immune system is activated and sends lymphocytes and other white blood cells to infected tissues, causing inflammation and producing antibodies against the virus. In some patients, the immune system’s response may cause more local tissue injury than the virus itself. Myocardial edema (tissue swelling) with decreased heart function and arrhythmias can result.

The impact of COVID-19 on the heart and the much higher risk of myocarditis among patients with COVID-19 compared to patients without COVID-19 underscores the importance of prevention of spread of the virus. Vaccines against SARS-CoV-2 have been demonstrated to be safe and effective at preventing serious infection. In May 2021, a study published in the New England Journal of Medicine reported a vaccine efficacy of 100% among more than 1,000 fully vaccinated children age 12 to 15 years of age. The children were followed up to 6 months from the second dose. This study was performed prior to the arrival of the Omicron variant and more recent experience in children infected with this variant show that breakthrough infections do occur. Unfortunately, peer-reviewed published data for the efficacy of the vaccine against the Omicron variant are lacking at this time. A larger study of 2,200 vaccinated children 5 to 11 years of age found the vaccine to be safe and had an efficacy of 91%. Currently, the American Academy of Pediatrics and the CDC recommend that all adolescents ages 5 and older receive the COVID-19 vaccine.

Recently, rare cases of vaccine-associated myocarditis have been reported in adolescent males usually following the second dose. These boys typically present with complaints of chest pain with or without elevated troponin levels in the blood. As of June 2021, the Vaccine Adverse Event Reporting System (VAERS) reported 1,226 cases of myocarditis after COVID-19 vaccination. The median age was 26 years and the median time to onset of symptoms was 3 days after the vaccination. Cases were reported after both the Pfizer- BioNTech and Moderna vaccines. Among a subset of 323 patients determined to have myocarditis after the vaccines, the vast majority were male (90%) with mild clinical cases and none had died. Upon reviewing the evidence of myocarditis after the vaccine, the Advisory Committee on Immunization Practices of the CDC determined that the benefits of the mRNA COVID-19 vaccines clearly outweigh any risks.

The question of when is it safe for children to return to playing sports and physical activity has received a great deal of attention during the pandemic. The American Academy of Pediatrics has created guidance for pediatricians when recommending return to play for children who developed COVID-19. In general, children who never developed symptoms (chest pain, palpitations, shortness of breath, fainting) while infected may return to play following a period of quarantine. It is recommended that the primary care physician assess the child at least once. For children who were symptomatic, return to activity depends on the severity and resolution of symptoms and may range from 10 days to 6 months. Parents should seek the advice of their primary care team before allowing their child to return to physical activity.

References:

Boehmer TK, Kompaniyets L, Lavery AM, et al. Association between COVID-19 myocarditis using hospital-based administrative data—United States, March 2020-January 2021. MMWR 2021;70:1128-32.

Siripanthong B, Nazarian S, Muser D, et al. Recognizing COVID-19–related myocarditis: The possible pathophysiology and proposed guideline for diagnosis and management. Heart Rhythm 2020;17:1463–1471.

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 2021;70:977-982.

Fenck RW, et al. Safety, immunogenicity, and efficacy of the BNT162b2 Covid-19 vaccine in adolescents. N Engl J Med 2021; 385:239-250.

Walter EB, et al. Evaluation of the BNT162b2 Covid-19 vaccine in children 5 to 11 years of age. N Engl J Med 2022;386:35046.