SARS-CoV-2 Omicron variant causes mild pathology in the upper and lower respiratory tract of Syrian golden hamsters (Mesocricetus auratus)

Abstract Since its discovery in 2019, multiple variants of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) have been identified worldwide. The present study investigates virus spread and associated pathology in the upper and lower respiratory tracts in the early phase of SARS-CoV-2 Omicron infection in the Syrian golden hamster (Mesocricetus auratus) in comparison to previous identified variants of concern (VOCs). Syrian golden hamsters were infected intranasally with SARS-CoV-2 614G or with VOCs Gamma, Delta and Omicron. Pathological changes both in the upper and lower respiratory tract of VOC Omicron infected hamsters were milder than those caused by the other investigated strains. VOC Omicron infection caused only a mild rhinitis with mild involvement of the olfactory epithelium and minimal lesions in the lung with frequent sparing of the alveolar compartment. Similarly, viral antigen detection as well as infectious SARS-CoV-2 titers were lower in upper and lower respiratory tract of VOC Omicron infected hamsters. These findings demonstrate that the SARS-CoV-2 VOC Omicron variant has a decreased pathogenicity for both the upper and lower respiratory tract of Syrian golden hamsters.