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Phylogenetic tree of the HA (positions 98 to 1059) gene of the H3N2 swine influenza viruses in China from 1970 to 2006. The unrooted phylogenetic tree was generated by the distance-based neighbor-joining method using MEGA 3.1. The reliability of the tree was assessed by bootstrap analysis with 1,000 replications; only bootstrap values of >90% are shown. Different lineages and sublineages are indicated by different colors.
