In addition, it has been shown that BA.1 variants are less pathogenic than the other circulating VOCs in both mice and hamsters46,85–87, which is consistent with clinical observations in humans that Omicron virus is associated with milder clinical severity88, although the widespread SARS-CoV-2 immunity from vaccination or natural infection has been shown to contribute in part to this phenomenon89. This evidence concerns the gene CFB and infection.