You can help prevent influenza by getting immunized with an influenza vaccine each year, ideally in October or November. The inactivated influenza vaccine(What is a PDF document?) commonly known as the "flu shot," is given by injection. This form of the vaccine effectively prevents most cases of the flu, although success rates vary according to age, health status, and how closely the virus strains contained in the vaccine match those that are circulating through the population.

Even if a flu shot does not prevent the flu, the vaccine can reduce the severity of flu symptoms and decrease the risk of complications. Studies have found that the flu shot results in fewer days missed from work and fewer visits to a doctor for respiratory infections, and it reduces the number of people who develop complications from the flu, such as pneumonia.⁵

In spite of these results, many people choose not to get a flu shot. Some do not get the shot because of myths they believe about the flu or the vaccine. The flu shot may cause side effects in some people, but they are usually minor and do not last long.

For help deciding if the flu shot is right for you, see:

Should I get a flu shot?

An alternative to the flu shot is now available. In 2003, the U.S. Food and Drug Administration (FDA) approved a nasal spray flu vaccine(What is a PDF document?). Healthy people ages 2 through 49 years can usually get the nasal spray form of the vaccine, called FluMist. The nasal spray vaccine contains components of live viruses, so it should not be given to people with certain long-term (chronic) health conditions, such as heart or lung problems. Close contacts of these people in high-risk categories can be given either type of vaccine, with one rare exception. Immunization with the inactivated virus (flu shot) is preferred over the nasal spray vaccine for close contacts of people with severely impaired immune systems during times when a protected environment is needed. This avoids the risk of transmitting an active flu virus from the nasal spray vaccine. If the nasal spray vaccine is used, contact with anyone in this high-risk group should be avoided for 7 days. For close contacts of people in all other high-risk categories, vaccination with either the flu shot or the nasal spray is considered safe.⁵

You should not use FluMist if you:

• Have heart disease.
• Have lung disease, including asthma.
• Have diabetes or kidney disease.
• Have a disease or take a medicine that causes problems with your immune system.
• Have had Guillain-Barré syndrome.
• Are pregnant.
• Have ever had an allergic reaction to FluMist or to eggs.
• Are younger than age 20 and you take aspirin or products with aspirin in them.