ACE2 and infection: Further studies are needed to (a) better understand the kinetics of infection and ensuing immune responses in BALB/c mice; (b) determine whether/which other variants can infect laboratory mice and the genetic determinants required, and (c) reveal the basis of the acquired ability of the virus to infect laboratory mice, i.e., an increased affinity to mACE2 specifically or to ACE2 across species (including hACE2).