Case report of acute myocarditis after administration of coronavirus disease 2019 vaccine in Japan

BACKGROUND: The worldwide spread of coronavirus disease 2019 (COVID-19) is still not under control and vaccination in Japan started in February 2021, albeit later than in Europe and the USA. The COVID-19 vaccination frequently leads to minor adverse reactions, which may be more intense after the second dose. The number of case reports of myocarditis following COVID-19 vaccination have been recently increased. CASE SUMMARY: We report a case of a 26-year-old healthy man who presented to our hospital with chest pain on 24 May 2021, 4 days after his second COVID-19 vaccination. The electrocardiogram showed ST elevation with upward concavity in I, II, aVL, aVF, V4 to V6, and small Q wave in II, III, aVF. Laboratory studies revealed elevation of troponin I, creatine kinase, C-reactive protein, and negative viral serologies. Acute aortic dissection and pulmonary thromboembolism were ruled out by contrast-enhanced thoracoabdominal computed tomography. An urgent coronary angiogram was performed because an acute coronary syndrome was suspected, but no significant stenosis was found. Cardiac magnetic resonance imaging demonstrated oedema and late gadolinium enhancement of the left ventricle in a mid-myocardial and epicardial distribution. DISCUSSION: Although the temporal association does not prove causation, the very short span between the second vaccination and the onset of myocarditis suggests that this acute myocarditis seemed to be an adverse reaction to COVID-19 vaccine. To the best of our knowledge, this is the first published case of acute myocarditis following COVID-19 vaccine in Asia.