Finally, immunohistochemistry staining for SARS-CoV-2 viral nucleocapsid protein revealed a 2–3-fold increase in percent area staining positive for viral nucleocapsid in the K18-hACE2 and hACE2 mice relative to C57BL/6J mice and an over ten-fold increase in signal relative background staining in the mock infections, supporting increased lung viral burden in both the K18-hACE2 and hACE2 mice. Here, KRT18 is linked to infection.