SERPINA1 and COVID-19: This study aimed to identify whether the presence of alleles A (rs2892474) and T (rs17580) of the SERPINA1 gene, and allele T (rs35705950) of MUC5B in patients with COVID-19 are associated with severe forms of the disease in the Mexican population, and to evaluate the concentration of mucin 5B in the plasma of patients with severe COVID-19.