Figure. Phylogenetic relationships among 2,492 complete hemagglutinin (HA) genes of pandemic (H1N1) 2009. At the center, the whole neighbor-joining tree. On the left, enlargement of 2 regions of the tree including pure monophyletic D222G clusters, indicated in blue. On the right, enlargement of the monophyletic D222E virus cluster, including 98% of the global 222E isolates (red box). E222G variant isolates, as examples, respectively, from Italy (4), Norway (1), Sweden, and the United Kingdom, are indicated in blue. The sequence labels represent the Global Initiative on Sharing All Influenza Data serial numbers; those of particular interest for this study are indicated by the strain name or country of origin.