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. Thousands of people die each year from influenza-related illnesses.
Most deaths caused by influenza are in elderly people.
The viruses that cause influenza change often, and protection declines within a year after vaccination. So people who need the vaccine should get it every year. The vaccine begins to protect you after 1 to 2 weeks and protection may last up to one year. Influenza is most common in the U.S. from December to April, so it is best to get the vaccine in the fall. People 9 years and older need one shot each influenza season, while children less than 9 years old may need a second shot after one month.