Fig 2.

HA amino acid alignment for seasonal H1N1 viruses isolated between 2004 and 2009 (excluding pandemic A/H1N1/2009). A gap was inserted to correspond to H1 numbering. Colors indicate the strains that belong to the groups with the corresponding colors in the HA phylogenetic tree (Fig. 1A). Black frames indicate the amino acid substitutions from 2004 to March 2009 that were studied; NC/99 is included for reference (residues 146, 253, and 267 were excluded because the former two were the same in the other strains as in NC/99 and the last residue has been conserved since 2006). Black and red horizontal lines indicate the HA1 and HA2 domains, respectively.