About Influenza

Influenza (flu) is a contagious respiratory illness caused by influenza viruses. It circulates every fall and winter. Most people recover within a few days to two weeks, but flu can be serious, especially for higher-risk groups.

Flu tends to come on suddenly. Common symptoms include fever, cough, sore throat, body aches, headache, and fatigue; some people, especially children, may also have vomiting or diarrhea. Symptoms usually begin one to four days after exposure.

Who is at higher risk

Some people are more likely to have serious complications and should take extra care:

Prevention & vaccines

A yearly flu vaccine is the best protection and is recommended for everyone 6 months and older, ideally by the end of October. Layer on everyday steps like staying home when sick and washing hands.

See full details, including where to get vaccinated, on the Prevention & Vaccines page.

Treatment & when to seek care

Most people recover with rest and fluids. Antiviral medicines (such as oseltamivir) can shorten illness and lower the risk of complications when started early — ideally within about two days of symptoms — and are especially important for higher-risk patients.