Note: “Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2019–20 Influenza Season” has been published. CDC recommends annual influenza vaccination for everyone 6 months and older with any licensed, influenza vaccine that is appropriate for the recipient’s age and health status, (IIV, RIV4, or LAIV4) with no preference expressed for any one vaccine over another. Content on this website is being updated to reflect this most recent guidance. More information about the upcoming 2019-2020 flu season is available.
Influenza (flu) is a contagious respiratory illness caused by influenza viruses. 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, 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 each year.
Flu and flu vaccine
Learn more about different types of influenza viruses and how these viruses can change over time.
Seasonal Influenza (Flu) frequently asked questions