Genetic association studies between KIR and influenza infection progression with the 2009 pandemic influenza A (H1N1) virus showed a higher frequency of KIR2DL2 and/or KIR2DL3 in combination with their cognate HLA-C1 ligand and KIR2DL1 without the presence of HLA-C2 ligands in patients with severe influenza infection [185]. This evidence concerns the gene KIR2DL3 and influenza.