日本小児循環器学会雑誌 Pediatric Cardiology and Cardiac Surgery

Myocarditis is a known adverse reaction against messenger RNA (mRNA) coronavirus disease 2019 (COVID-19) vaccines, but the method for the diagnosis of postvaccination myocarditis has not been established. We report a child case of postvaccination myocarditis, which was diagnosed by abnormal blood test results alone. The patient was a previously healthy 13-year-old boy who received the second dose of mRNA COVID-19 vaccine (BNT162b2). Two days after vaccination, he experienced chest pain. He was taken to the hospital on the same day, but no abnormal physical findings were noted. Electrocardiogram and echocardiogram were both normal, but cardiac enzymes were elevated. We diagnosed him with postvaccination myocarditis. The symptoms and elevation of cardiac enzymes improved with no medical treatment. Throughout the disease course, only abnormal blood test values were noted on the acute phase; therefore, the diagnosis could not be confirmed. The incidence of postvaccination myocarditis is expected to increase with the increase in the vaccinations to younger age groups and additional vaccinations. To estimate the exact frequency and long-term prognosis of postvaccination myocarditis, accumulation of cases through proactive investigation, including blood tests, are desirable.