TY - JOUR T1 - Reduced Pathogenicity of the SARS-CoV-2 Omicron Variant in Hamsters JF - bioRxiv DO - 10.1101/2022.01.02.474743 SP - 2022.01.02.474743 AU - Katherine McMahan AU - Victoria Giffin AU - Lisa H. Tostanoski AU - Benjamin Chung AU - Mazuba Siamatu AU - Mehul S. Suthar AU - Peter Halfmann AU - Yoshihiro Kawaoka AU - Cesar Piedra-Mora AU - Amanda J. Martinot AU - Swagata Kar AU - Hanne Andersen AU - Mark G. Lewis AU - Dan H. Barouch Y1 - 2022/01/01 UR - http://biorxiv.org/content/early/2022/01/03/2022.01.02.474743.abstract N2 - The SARS-CoV-2 Omicron (B.1.1.529) variant has proven highly transmissible and has outcompeted the Delta variant in many regions of the world1. Early reports have also suggested that Omicron may result in less severe clinical disease in humans. Here we show that Omicron is less pathogenic than prior SARS-CoV-2 variants in Syrian golden hamsters. Infection of hamsters with the SARS-CoV-2 WA1/2020, Alpha, Beta, or Delta strains led to 4-10% weight loss by day 4 and 10-17% weight loss by day 6, as expected2,3. In contrast, infection of hamsters with two different Omicron challenge stocks did not result in any detectable weight loss, even at high challenge doses. Omicron infection still led to substantial viral replication in both the upper and lower respiratory tracts and pulmonary pathology, but with a trend towards higher viral loads in nasal turbinates and lower viral loads in lung parenchyma compared with WA1/2020 infection. These data suggest that the SARS-CoV-2 Omicron variant may result in more robust upper respiratory tract infection but less severe lower respiratory tract clinical disease compared with prior SARS-CoV-2 variants.Competing Interest StatementThe authors have declared no competing interest. ER -