CDC has estimated the burden of flu since 2010 using a mathematical model that is based on observed rates of laboratory-confirmed influenza-associated hospitalizations collected through a surveillance network that covers approximately 8.5% of the U.S. population (~27 million people).
The 2018-2019 flu season is the first season CDC has reported in-season burden estimates of flu in the U.S. These in-season estimates will be updated over the course of the flu season.