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.
- People at High Risk from Flu - Some people are more likely to get flu complications that result in being hospitalized and occasionally result in death.
- How Flu Spreads - How the virus spreads and how long people may be contagious.
- The Flu Season - General information on regular flu seasons in the United States.