Phylogeny of of the NA gene of seasonal A
influenza viruses. Phylogenetic analysis of the neuraminadase gene sequences of H1N1 viruses, using MEGA version 5 for constructing Maximum Likelihood Tree using the Tamura-nei evolutionary model. The prototype reference strains for each clade are colored in purple, the contemporary vaccine virus recommended for inclusion of the trivalent influenza vaccine for the 2008/2009 Northern Hemisphere winter is shown in blue ; Viruses from Dakar, Senegal, are shown in red. The group indicated by the asterix carries the H275Y amino acid substitution.