Regarding HLA ligands, a strong significant increase in the frequencies of HLA-C1 in COVID-19 (p = 0.0003) and HIV (p = 0.015) groups and of HLA-C2 in COVID-19 (p = 0.007), HIV (p = 0.021) and HBV (p < 0.0001) individuals was observed, which means a higher percentage of C1/C2 heterozygotes than the control population. Here, C2 is linked to COVID-19.