This vaccine protects people against the flu.

The flu is a contagious respiratory disease caused by an influenza virus. In the U.S., flu outbreaks typically occur in winter months. Symptoms include fever, chills, sore muscles, and cough. Thousands of people in the U.S. die each year from the flu or its complications. Most of those who die are the elderly, young children, or people with compromised immune systems.

See article on the flu for more information.

The viruses that typically cause the flu are primarily categorized as influenza type A or type B. Influenza type B does not change much over time, but type A can mutate rapidly. Therefore, a new form of the flu vaccine must be developed each year to protect people for the exact strain that is expected to be most prevalent.

All the influenza viruses in the flu shot are killed (inactive), so it is not possible to get the flu from this type of vaccine. However, some people do experience a low-grade fever for a day or two after the shot as their immune systems gear up to recognize the virus. (See "Risks" section in this article.)

A new nasal spray-type flu vaccine called FluMist is proving to be effective and safe in healthy people aged 2 to 49 years old. The FDA-approved vaccine helps the lining of the nose fight off actual viral infections. (FluMist uses a live, weakened virus instead of a dead one like the flu shot.) In one study, the nasal spray provided protection against the flu in up to 93% of children. It should not be used in those who have asthma or children under age 5 who have repeated wheezing episodes.

Flu vaccines are generally given at the beginning of the "flu season" -- usually late October or early November in the U.S. People traveling to other countries should be aware the flu may occur at different times.

IMMUNIZATION SCHEDULE

According to the U.S. Centers for Disease Control and Prevention, anyone who wants to reduce their risk of the flu can get a flu shot. The flu shot is approved for anyone older that 6 months of age. Some people have a higher risk of the disease. You should be vaccinated each year if you:

• Are 50 or older
• Have chronic lung or heart disease
• Have sickle cell anemia and other hemoglobinopathies
• Live in a nursing home or extended care facilities
• Live in any type of housing where there are chronic health problems
• Have kidney disease, anemia, severe asthma, diabetes, or chronic liver disease
• Have a weakened immune system (including those with cancer or HIV/AIDS)
• Receive long-term treatment with steroids for any condition
• Expect to be past the 3rd month of pregnancy during the flu season (you may want to consider requesting the mercury-free flu vaccine)

Children and teenagers receiving long-term aspirin therapy and children between the age of 6 months and 2 years should also receive a flu shot each year. Mercury-free vaccines are preferred in younger children.

The flu shot is encouraged for:

• Health care providers who work in high-risk settings
• Direct contacts or caretakers of high-risk individuals
• People who have in-home contact with children who are younger than 5 years old
• People who provide essential community services
• People living in dormitories or other crowded conditions
• Anyone who wants to reduce their change of getting influenza

Children under age 9 require two shots 1 month apart the first time that they receive influenza vaccine. Older children and adults only require a single shot each year.

BENEFITS

Most people achieve protection from the flu approximately 2 weeks after receiving the vaccine.

Immunization of high-risk people reduces the risk of death from the flu. Immunization of those caring for high-risk people reduces the risk of spreading the disease to other people who may have a higher than average risk for complications.

RISKS

Most people have no side effects from the flu shot. Soreness at the injection site or minor aches and low grade fever may be present for several days.

Unlike the swine flu vaccine used in 1976, flu vaccines in recent years have shown no association with Guillain-Barre syndrome (GBS) in children, and an extremely small increase in the risk of GBS in adults. This risk is far outweighed by the number of severe flu cases prevented by immunization.

As is the case with any drug or vaccine, there is a rare possibility of allergic reaction.

WHO SHOULD NOT RECEIVE A FLU VACCINE

According to the CDC, some people should not be vaccinated without first talking to a doctor. In general, you should not get a flu shot if you:

• Had a severe allergic reaction to chickens or egg protein
• Have a fever or illness that is more than "just a cold"
• Had a moderate to severe reaction after a previous flu vaccine
• Are a woman who is, or might be, in the first trimester of pregnancy (first 3 months of pregnancy)
• Have ever been paralyzed due to Guillain-Barre Syndrome

If you meet any of the above criteria, ask your doctor if a flu vaccine is safe for you.

Buonagurio DA, Bechert TM, Yang CF, et. al. Genetic stability of live, cold-adapted influenza virus components of the FluMist/CAIV-T vaccine throughout the manufacturing process. Vaccine. 2005 Nov 21; [Epub ahead of print] .

Harper SA, Fukuda K, Uyeki TM, Cox NJ, Bridges CB; Advisory Committee on Immunization Practices (ACIP), Centers for Disease Control and Prevention (CDC). Prevention and control of influenza. Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2005 Jul 29;54(RR-8):1-40. Erratum in: MMWR Morb Mortal Wkly Rep. 2005 Aug 5;54(30):750.

US Food and Drug Administration. FDA Approves Nasal Influenza Vaccine for Use in Younger Children. Rockville, MD: National Press Office; September 19, 2007.