Influenza vaccine (the flu shot) can prevent influenza. For most people, the vaccine prevents serious influenza-related illness, however, it will not prevent "influenza-like" illnesses caused by other viruses. Influenza viruses are constantly changing, therefore influenza vaccines are updated every year, and annual vaccinations are recommended.
Protection lasts as long as a year. It takes up to two weeks following vaccination for immunity to develop. The flu shot is given by injection to people age six months and older. People should plan to be vaccinated in October or November.