In SARS-CoV-2, the titer and types of natural antibodies (IgM vs. IgG), spatial hindrance of viral attachment to its receptor by the bound antibodies, and destruction of the antibody coated viruses by the complement, have been presented as explanations for the lower incidence of infection in blood group O individuals [26,27,28,29,30]. The gene discussed is CD40LG; the disease is infection.