Suspected Myocarditis after mRNA COVID-19 Vaccination among South Korean Adolescents

Objective Since vaccination for coronavirus disease 2019 (COVID-19) has been initiated, rare cases of COVID-19 mRNA vaccination-associated myocarditis (VAM) have been reported worldwide. This study aimed to report the short-term outcomes and the clinical presentation of VAM in South Korean adolescents.Methods In this prospective multicenter study across five tertiary hospitals in South Korea, patients aged 12 to 17 years with symptoms of VAM were included from October 18, 2021, to April 30, 2022. We performed laboratory tests, electrocardiography, chest radiography, echocardiography, and cardiac magnetic resonance imaging studies on these patients.Results A total of 14 patients were diagnosed with VAM during the study period. The median age of the patients was 15.2 years (interquartile range [IQR], 14.6-15.9) and 11 patients (78.6%) were male. All patients had received a messenger RNA Pfizer-BioNTech COVID-19 vaccine. The median latent period from vaccination to symptom onset was 1 (range, 0-8; IQR, 0.8-3.5) day. Chest pain was the most common symptom (11/14, 78.6%), and the median duration of symptoms was 1 week. Except for one patient (7.1%) who was admitted to intensive care unit, most patients (13/14, 93.8%) had a minor and short clinical course without an intensive treatment including an immune modulator.Conclusion VAM in South Korean adolescents had self-limiting clinical courses as reported by previous studies. Despite the small number of cases, our findings, consistent with previous studies, revealed that East Asian adolescents might have a similar or even milder clinical course than adolescents of other ethnicities.