Table 2 shows the distribution features of the ABO blood types in the mild and critical cohorts. The proportion of blood group A in patients with COVID-19, 35.76% in the mild cohort and 39.22% in the critical cohort, was significantly higher than that in the reference population (p = 0.000 and p = 0.005, respectively), which comprised half a million Han Chinese individuals from China (33). The gene discussed is ABO; the disease is COVID-19.