Phylogenetic analysis
H9N2 AIV isolates evolved at steady mean evolutionary rates, 8.036 × 10-3 (95% HPD: 6.058 × 10-3~ 9.702 × 10-3) in recent years in China. All randomly down-sampling sequences belonged to clade 15 of H9N2-AIV. The sequences were diversified into 3 additional subclades (A, B and C) based on significant nucleotide differences, with subclade C comprising the predominant branch (Figure 1).