To investigate the role of the serine protease TMPRSS2 after infection with SARS-CoV-2, C57BL/6 wild-type (wt) and TMPRSS2 knock-out (TMPRSS2 KO) mice were infected intranasally (i.n.)with SARS-CoV-2 Beta (B.1.351) or Omicron (B.1.1.529) and monitored for 3 days (Figure 1A); during this time, the mass loss and clinical score were determined (Figure 1B–I). The gene discussed is TMPRSS2; the disease is infection.