Figure 3. Phylogenetic analysis of influenza pandemic (H1N1) 2009 viruses neuraminidase (NA) (A) and hemagglutinin (HA) genes (B). Most pandemic (H1N1) 2009 viruses possessed the amino acid substitutions S203T in HA and V106I and N248D in NA. Red, oseltamivir-resistant pandemic (H1N1) 2009 from Japan; green, oseltamivir-resistant pandemic (H1N1) 2009 from outside Japan; black, oseltamivir-susceptible (OS) pandemic (H1N1) 2009; purple, 2009–10 current vaccine strains. The sampling month of each isolate is listed following the strain name. The phylogenetic tree of NA and HA genes was constructed by using the neighbor-joining method. Scale bars indicate nucleotide substitutions per site.