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Seasonal Influenza: Flu Basics

Note: On June 22, 2016, CDC’s Advisory Committee on Immunization Practices (ACIP) recommended a change to U.S. influenza vaccination policy for 2016-2017. The ACIP recommendation must be reviewed and approved by CDC’s Director, and the final recommendations will be published in a CDC Morbidity and Mortality Weekly Report (MMWR), in late summer or early fall. The content of this website will be reviewed and updated prior to the 2016-2017 influenza season.

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 for serious flu complications. The best way to prevent the flu is by getting vaccinated each year.

The upcoming season's flu vaccine will protect against the influenza viruses that research indicates will be most common during the season. This includes an influenza A (H1N1) virus, an influenza A (H3N2) virus, and one or two influenza B viruses, depending on the flu vaccine.

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