CTSL and infection: Although several studies support the view that TMPRSS2-dependent early entry route is more efficient and results in a more productive infection than the cathepsin L-activated mechanisms for some CoV strains (Shirato et al., 2017, 2018), other studies indicate that more recent Omicron SARS-CoV-2 variants favor the low-pH endosomal entry route (Meng et al., 2022).