Figure 3: Branching profiles of avian H5N1 influenza viruses analyzed in the selection of target vaccine strain (A). Evolutionary analysis was performed ad described previously (15). Arrow 1 indicated vaccine strain and arrow 2 showed the newest branch of clade 2, 3. Comparison of the evolutionary rates of H5 HA genes of avian influenza viruses belonging different clades for the selection of vaccine strain (B). The evolutionary rate was estimated at 0.0050 substitutions per site per year. The evolutionary trajectory of viruses belonging to subclade 2. 3 viruses have evolved discontinuously (green and blue lines). The duck-Fukushima strain belonging to subclade (red symbol) was selected as the target vaccine preparation.