It can cause fever, chills, headache, cough, sore throat, and muscle aches. Flu can lead to pneumonia and death. Flu can affect people of any age. Occasionally people with flu will need to be hospitalized. Thousands of people die each year from flu-related illnesses.
Most deaths caused by flu occur in the elderly population.
The viruses that cause influenza change often, therefore a new vaccine is developed each year. The vaccine begins to protect you 1 to 2 weeks after the injection and may last approximately 6 months to one year. Since flu viruses change frequently, the vaccine may not always cover them. Also, other viruses cause diseases that seem like influenza, and the vaccine does not protect against other viral diseases. There are risks associated with any medicine.