Evolution of Immune Evasion and Host Range Expansion by the SARS-CoV-2 B.1.1.529 (Omicron) Variant

Recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant B.1.1.529 (Omicron) has rapidly become the dominant strain, with an unprecedented number of mutations within its spike gene. However, it remains unknown whether these variants have alterations in their entry efficiency, host tropism, and sensitivity to neutralizing antibodies and entry inhibitors. In this study, we found that Omicron spike has evolved to escape neutralization by three-dose inactivated-vaccine-elicited immunity but remains sensitive to an angiotensin‐converting enzyme 2 (ACE2) decoy receptor. Moreover, Omicron spike could use human ACE2 with a slightly increased efficiency while gaining a significantly increased binding affinity for a mouse ACE2 ortholog, which exhibits limited binding with wild-type (WT) spike. Furthermore, Omicron could infect wild-type C57BL/6 mice and cause histopathological changes in the lungs. Collectively, our results reveal that evasion of neutralization by vaccine-elicited antibodies and enhanced human and mouse ACE2 receptor engagement may contribute to the expanded host range and rapid spread of the Omicron variant.