Here, we report a case of acute severe hepatitis in which adenovirus type 2 (AV2) was identified and HLA-DRB1 04:01 was detected in the host; this genotype was suspected to be the immunological background for factors contributing to the development of hepatitis following the coronavirus disease 2019 (COVID-19) pandemic. The gene discussed is HLA-DRB1; the disease is hepatitis A virus infection.