Figure 1.

Phylogenic tree of the HA genes of (A) B/Yamagata‐ and (B) B/Victoria‐lineage viruses isolated in Japan during the 2017‐2018 and 2018‐2019 influenza seasons. The tree was built using the neighbor‐joining method with 1000 bootstrap replicates. Bootstrap values ≥ 70 are displayed on the branches. The month during which the clinical specimens were collected is shown after each strain name. The scale bar shows a 1% nucleotide change between close relatives. A and B, Influenza B isolates examined in this study are shown in blue. Vaccine and vaccine‐related strains are indicated in red. The black circle symbol indicated the viruses that were subjected to the HI assay. B, The Δ162‐163 and Δ162‐164 indicate viruses possessing the two‐amino‐acid deletion at positions 162 and 163 in HA and viruses possessing the three‐amino‐acid deletion at positions 162‐164 in HA, respectively