The 2017-2018 flu season was a flu season of high severity in the United States. Influenza-like illness (ILI) has a high rate of outpatient and emergency clinic visits, and a high rate of influenza-related hospitalizations, and influenza activities have been on the rise for a long period of time and are widely distributed geographically. In 2017, the Centers for Disease Control and Prevention began using a new method to classify seasonal severity and applied the method to the seasons from 2003-2004 to 2016-2017. The 2017-18 season was the first season to be classified as highly serious among all age groups. 