It is caused by a virus. The disease comes on suddenly, with fever, chills, cough, general aches and pains, and a feeling of tiredness and weakness. Influenza symptoms usually last for a few days to a week and go away without treatment. However, in some people influenza can cause severe illness or death. It is estimated that more than 10,000 Americans die of influenza each year.
Influenza spreads easily from person to person.
It is spread by tiny droplets that come from a person's mouth and nose when they cough and sneeze. It can also spread indirectly, by touching objects contaminated with discharges from an infected person's nose and throat. Symptoms usually begin 1 to 3 days after exposure. It is recommended that influenza vaccine be given every year, preferably in late September or early October, just before the usual time that outbreaks begin. Persons at highest risk of infection or its complications should get the vaccine every year.