Mutation profile analysis suggests that the Omicron variants may have arisen through evolution via mouse host.4 In this study, our biochemical data confirmed that both BA.1 and BA.2 spike trimers are able to bind with high affinity to mouse ACE2 and cat ACE2, while the original WT spike binds well to cat ACE2 but not to mouse ACE2, indicating high susceptibility of mouse and cat to BA.1 and BA.2 infections (Fig. 7c). The gene discussed is ACE2; the disease is infection.