Both the lungs and brains of naïve mice showed high levels of virus at day 6 after infection (log-transformed mean titers of 4.2 PFU/g in the lungs and 8.8 PFU/g in the brains) (Fig. 4, F and G), consistent with previous reports of SARS-CoV-2 infection in K18-hACE2 mice (49, 51). This evidence concerns the gene KRT18 and infection.