Weak HLA-A alleles with a low number of binding repertoires of SARS-CoV-2 peptides had an exponential correlation with the severity rate. The reason for the exponential approximation was that the weak HLA-A frequency showed a positive linear correlation with the infection rate as well as the infection rate with the severity rate. Weak alleles with a low number of binding repertoires in HLA-B alone do not correlate with the severity rate at all, but by forming a haplotype with weak HLA-A, the severity rate is stronger than that of weak HLA-A alone. The gene discussed is HLA-B; the disease is infection.