Influenza (also known as the flu) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and can cause death. Influenza is not a cold. Influenza usually comes on suddenly. People who have Influenza often feel some or all of these symptoms: fever, chills, cough, sore throat, runny or stuffy nose, body aches, headaches, and fatigue. Most people who get influenza will recover in a few days to two weeks. Some people can develop complications (such as pneumonia) as a result of influenza.
Infants and small children are more vulnerable to influenza and can become seriously ill. They can get pneumonia, bronchiolitis and are more likely to die from the flu.
Anyone can get influenza (even healthy people), and serious problems related to influenza can happen at any age, but some people are at high risk of developing serious complications. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and young children.