Myocarditis following the third dose of a COVID-19 mRNA vaccination in an older woman

Myocarditis is a group of inflammatory diseases that primarily affect the myocardium. It includes various pathological conditions. In addition to viruses, which are the main etiological agents, other causal agents, including bacteria, toxic substances, autoimmunity, and drugs, including vaccines, can also induce the disease.In Japan, an outbreak of coronavirus disease 2019 (COVID-19) began in January 2020, and COVID-19 messenger RNA (mRNA) vaccinations have been widely used since February 2021.Myocarditis after vaccination is reported to be more common in young males, particularly after the second vaccination. We report the case of an 80-year-old woman with no history of cardiovascular disease who was hospitalized with acute pulmonary edema one week after receiving her third dose of mRNA vaccine. She had elevated myocardial markers, new complete left bundle branch block, and a decreased left ventricular ejection fraction relative to before the onset; however, there was no stenosis or coronary artery occlusion that could have caused the disease. Although a myocardial biopsy could not be performed, myocarditis after vaccination was diagnosed based on detailed clinical findings. With noninvasive positive pressure ventilation and diuretics without steroids, the patient improved and was discharged on the 11th day. However, 1.5 years later, she developed a complete atrioventricular block and a permanent pacemaker was implanted. This case suggests that even older women can develop myocarditis after the third vaccination dose. We should carefully consider whether vaccination should be administered, even in older patients.