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Influenza vaccines
Influenza vaccines



This vaccine protects people againstĀ the flu .

Alternative Names:

Vaccine - influenza; Immunization - influenza; Flu shot; Flu vaccine


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 against the exact strains that are expected to be most prevalent.

There are two types of flu vaccines: a flu shot and a nasal spray-type vaccine.

The flu shot contains killed (inactive) viruses, so it is not possible to get the flu from this type of vaccine. However, some people do get a low-grade fever for a day or two after the shot as their immune systems gear up to recognize the virus. The flu shot is approved for people age 6 months and older.

A nasal spray-type flu vaccine called Flutist uses a live, weakened virus instead of a dead one like the flu shot. It is approved for healthy people aged 2 to 49. The vaccine helps the lining of the nose fight off actual viral infections. 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.. They may also be given later in the winter, as late as March.

People traveling to other countries should be aware that the flu may occur at different times.


According to the U.S. Centers for Disease Control and Prevention, anyone who wants to reduce their risk of the flu should get a flu vaccine.

Older children and adults only require a single shot each year. However, children under age 9 need two shots 1 month apart the first time they receive flu vaccine or if they have not previously received two doses during one flu season.

Some people have a higher risk of the disease.

The following people should get a flu vaccine every year:

  • Children between the ages of 6 months and 18 years
  • Children over age 5 who have a higher risk for serious illness
  • Household contacts and caregivers of children or adults with high-risk conditions (Breast-feeding women may receive the vaccine.)

You should be vaccinated each year if you:

  • Are 50 or older
  • Have chronic lung or heart disease
  • Have sickle cell anemia or other hemoglobinopathies
  • Live in a nursing home or extended care facilities
  • Live with people who have 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
  • Are a pregnant woman
  • Are a woman who will be pregnant during flu season

The flu shot is encouraged for:

  • Health care providers
  • 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
  • Any adult ages 18 - 50 who wants to reduce their chance of getting influenza


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


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. Data indicates the flu vaccine does not harm the fetus when given to a pregnant women, nor does it affect reproductive health.


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
  • 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.


American Academy of Pediatrics Committee on Infectious Diseases. Recommended immunization schedules for children and adolescents -- United States, 2008. Pediatrics. 2008 Jan;121(1):219-20.

Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2008. MMWR. July 17, 2008/57(Early Release);1-60.

Recommended Immunization Schedule for Persons Aged 7-18 Years -- United States, 2008. MMWR. October 19, 2007/56(41);Q1-Q4.

Advisory Committee on Immunization Practices. Recommended adult immunization schedule: United States, October 2007-September 2008. Ann Intern Med. 2007 Nov 20;147(10):725-9.

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

Review Date: 8/5/2008
Reviewed By: A.D.A.M. Editorial Team: David Zieve, MD, MHA, Greg Juhn, MTPW, David R. Eltz. Previously reviewed by David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine (6/18/2008).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

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Phone: (603) 742-5252
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