It is caused by a virus that spreads from infected persons to the nose or throat of others. Most people are ill with influenza for only a few days, but some get much sicker and may need to be hospitalized.
Influenza causes thousands of deaths each year, mostly among the elderly.
Influenza vaccine can prevent influenza. Influenza viruses change often. Therefore, influenza vaccine is updated each year to make sure it is as effective as possible. Protection develops about 2 weeks after getting the shot and may last up to a year. Residents of long term care facilities housing persons with chronic medical conditions.