Influenza ("flu") is a serious disease. It is caused by a virus that spreads from an infected person to the nose or throat of another.

Influenza can cause fever, sore throat, chills, cough, headache, and muscle aches. Anyone can get the flu. Most people are ill with influenza for only a few days, but some get much sicker and may need to be hospitalized. Influenza causes an average of 114,000 hospitalizations and 36,000 deaths each year in the United States, mostly among the elderly.

Influenza vaccine can prevent influenza.