MYH14 and myocarditis: The pathogenesis of postvaccination myocarditis remains unclear.[3,15] One theory is that the immune system is activated by the recognition of mRNA as an antigen.[24] The other theory is that antibodies against the spike glycoprotein contained in the vaccine cross-react with α-myosin and transglutaminase to elicit an immune response.[17,25] In this case, chronic thyroiditis and fatty liver were observed, and the possibility that this background contributed to the immunological abnormalities against the vaccine cannot be completely ruled out.