The analysis included all the clinical immunological and genetic variables found significantly associated (P value < 0.05 in univariate analysis) with the course of the viral infection: age ≥ 65 yr, gender, flu vaccine, concomitant autoimmune diseases, KIR2DS2, KIR2DL2, KIR haplotype AA, the cA01/cA01 KIR gene content motifs, the KIR2DL2/HLA C1 and KIR2DS2/HLA C1 KIR-ligand combinations. This evidence concerns the gene KIR3DL1 and viral infectious disease.