To gain insight into the mechanisms of resistance/susceptibility to viral infections, in the present paper we investigated the distribution of individual KIR genes, their HLA ligands, KIR–HLA associations and KIR haplotypes in three different cohorts belonging to the same geographical area (Sicily): (i) symptomatic and asymptomatic subjects positive to SARS-CoV-2 in absence of COVID-19 vaccination; (ii) HIV-infected individuals who were receiving antiretroviral therapy; (iii) HBV-positive subjects with CHB [18]. The gene discussed is KIR3DL1; the disease is viral infectious disease.