Influenza (flu) is a contagious respiratory illness caused by influenza viruses, opens a new window. It can cause mild to severe illness. Serious outcomes of flu infection can result in hospitalization or death. Some people, such as older people, young children, and people with certain health conditions, opens a new window, are at high risk of serious flu complications.
There are two main types of influenza (flu) virus: Types A and B. The influenza A and B viruses that routinely spread in people (human influenza viruses) are responsible for seasonal flu epidemics each year.
The best way to prevent flu is by getting vaccinated, opens a new window each year.
Learn more: Centers for Disease Control – About Flu, opens a new window
U.S. Centers for Disease Control and Prevention
- Influenza (Flu), opens a new window
- Understanding the Influenza Viruses, opens a new window
- 2019-2020 U.S. Flu Season: Preliminary Burden Estimates, opens a new window