Influenza (also known as flu) is a contagious respiratory illness caused by flu viruses. It can cause mild to severe illness, and at times can lead to death. Flu is different from a cold. Flu usually comes on suddenly. People who are sick with flu often feel some or all of these symptoms; fever* or feeling feverish/chills (though, it's important to note that not everyone with flu will have a fever), cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, and fatigue (or tiredness).

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