It spreads when influenza viruses pass from an infected person to the nose or throat of others.
Influenza can cause fever, cough, chills, headache, muscle aches, sore throat.
It can lead to pneumonia and death. Influenza can make people of any age ill. Although most people are ill for only a few days, some have a much more serious illness and may need to be hospitalized. More than 20,000 Americans die each year from influenza-related illnesses. Most deaths caused by influenza are in elderly people.