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HA gene phylogeny of influenza A(H1N1)pdm09 viruses detected in Bulgaria during the 2015/2016 season. Reference viruses are indicated in bold and vaccine virus A/California/7/2009 in red. Bulgarian viruses detected in December 2015, January, February and March 2016 are indicated in purple, green, blue and pink, respectively. The tree is rooted at A/California/7/2009. Amino acid substitutions defining particular nodes are indicated and bootstrap values > 70% are shown in parentheses.
