The "current season" refers to the months of October through May. Data reported from Vaccine Immunization Information System (VIIS). Measure is calculated by (1) dividing the number of children (5 – 18 years of age) who received flu vaccine in the current season of the previous year by the total number of children (5 – 18 years of age) in the previous year; (2) dividing the number of children (5 – 18 years of age) who received flu vaccine in the current season of the present year by the total number of children (5 – 18 years of age) in the present year; and (3) subtracting the value in (1) from the value in (2).