The flu (influenza) is a serious disease. It is caused by a virus, which spreads through the air from infected persons to others through their nose or throat. The flu can cause fever, cough, chills, sore throat, headache and muscle aches.
People of any age can get the flu. Most people are ill with the flu for only a few days, but some become much sicker and may need to be hospitalized. The flu causes thousands of deaths each year, mostly among the elderly.
"SP565-Are You Due for the Flu Shot this Fall?," The University of Tennessee Agricultural Extension Service, 09-0090 SP565-10M-10/08(Rev) E12-5315-00-015-09, http://trace.tennessee.edu/utk_agexheal/36