This infection dose was similar to, or potentially even lower than, that of other transgenic mouse models, such as hACE2-expressing mice controlled by the K18 and HFH4 promoters, which were presently the prevailing promoters employed in SARS-CoV-2 infection studies (Jiang et al., 2020; Moreau et al., 2020; Rathnasinghe et al., 2020; Winkler et al., 2020; Yinda et al., 2021). The gene discussed is KRT18; the disease is infection.