Influenza (flu) is a potentially serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and flu can affect people differently, but during typical flu seasons, millions of people get flu, hundreds of thousands of people are hospitalized and thousands to tens of thousands of people die from flu-related causes. Flu can mean a few days of feeling bad and missing work, school, or family events, or it can result in more serious illness.