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Phylogenetic analysis of NA genes of influenza B virus isolates obtained during the 1999-2005 influenza season. The dendrogram of the 45 influenza B virus outbreak strains, with 24 reference strains from GenBank, of the NA gene using the neighbor-joining method with the DNADIST distance measure program (PHYLIP, version 3.573c). The percentage of bootstrap frequency of each branch in the tree is indicated. B/Lee/40 was included as an outgroup.
