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Phylogenetic analysis of HA1 amino acid sequences of human and avian H2 influenza virus isolates. The predicted HA1 (340 amino acids, including the signal peptides) sequences of 9 human and 22 avian isolates were used in the alignment and analyzed using Vector NTI. The phylogenetic tree was built using a nonrooted neighbor-joining method. The phylogenetic distance of each sequence from the nearest node was measured and is shown in parentheses.
