HCoV-OC43 is the most common species. A large prospective surveillance study conducted in Norway from 2006 to 2015 that enrolled all hospitalized children aged ≤16 years with respiratory tract infections revealed that HCoVs OC43 and NL63 were detected most frequently and were epidemic every second winter. HCoV-HKU1 was prevalent every second winter during the year when detection rates for HCoVs OC43 and NL63 were low; HCoV-229E was the least common.