Figure 2

The age distribution of Yamagata- and Victoria-lineage virus. The y-axis represents the proportion of Victoria-lineage (a) and Yamagata-lineage (b) in assembled ILI outpatients caused by influenza virus every month. The x-axis shows month from October 2011 to September 2017. The period from October to September next year is defined as one influenza seasons. The age group ≤5 years old was shown by a yellow lines; the age group 6–17 years old was shown by a green lines; the age group 18–59 years old was shown by a blue lines and the age group ≥60 years old was shown by a violet lines.