SERPINA1 and alpha 1-antitrypsin deficiency: Nonetheless, the geographical overlap between rates of AATD and severity of COVID-19 suggests that protease–antiprotease imbalance could play a critical role in the pathogenicity and virulence of SARS-CoV-2, or in the host response to COVID-19 infection, and that AAT could be a host protective factor against COVID-19.