Epidemiology of endemic human coronavirus infection during the COVID-19 pandemic.

Introduction: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a member of the coronavirus family that also includes endemic human coronaviruses (HCoVs) types OC43, HKU1, 229E, and NL63. HCoVs share extensive sequence homology with SARS-CoV-2. It has been assumed that HCoV infection occur primarily in winter and spring in Japan before the coronavirus disease 2019 (COVID-19) pandemic and that its frequency is the same for all age groups.