Who should get a flu shot? (top)

People at high risk for complications of the flu and people in close contact with them (including household members) should get the vaccine.

Recommendations of the Advisory Committee on Immunization Practices (ACIP)

Groups At Risk for Complications from Influenza

A yearly flu shot is recommended for the following groups of people who are at increased risk for serious complications from the flu:

• persons aged >50 years;*
• residents of nursing homes and other long-term care facilities that house persons of any age who have long-term illnesses;
• adults and children > 6 months of age who have chronic heart or lung conditions, including asthma;
• adults and children > 6 months of age who need regular medical care or had to be in a hospital because of metabolic diseases (like diabetes), chronic kidney disease, or weakened immune system (including immune system problems caused by medicine or by infection with human immunodeficiency virus [HIV/AIDS]);
• children and teenagers (aged 6 months to 18 years) who are on long-term aspirin therapy and therefore could develop Reye Syndrome after the flu; and
• women who will be more than 3 months pregnant during the flu season.

*People 50-64 years of age who do not have chronic (long-term) medical conditions might not be at high risk for serious complications from the flu.  However, about 26% of people aged 50-64 years have high-risk conditions and are at increased risk for flu-related complications.  Beginning in 2000, a flu shot was recommended for all people 50-64 years old each year to increase the number of high-risk 50-64 year olds who get a flu shot.

Because young, otherwise healthy children are at increased risk for influenza-related hospitalization, influenza vaccination of healthy children aged 6-23 months is encouraged when feasible.

Persons Who Can Give the Flu to People Who Are At High Risk for Complications

Persons with the flu can give it to other people. To help prevent flu among people at high risk for complications, the following people should get a flu shot:

• doctors, nurses, and other employees in hospitals and doctors' offices, including emergency response workers;
• employees of nursing homes and long-term care facilities who have contact with patients or residents;
• employees of assisted living and other residences for people in high-risk groups;
• people who provide home care to those in high-risk groups; and
• household members (including children) of people in high-risk groups.

Flu Prevention for the General Population

Anyone who wants to lower their chances of getting the flu (the shot can be administered to children as young as 6 months) can get a flu shot. Persons who provide essential community services (such as police, firemen, etc.) should consider getting a flu shot to minimize disruption of essential activities during flu outbreaks. Students or others in institutional settings (those who reside in dormitories) should be encouraged to get a flu shot.

Who should not get a flu shot? (top)

Talk with a doctor before getting a flu shot if you:

1) Have ever had a severe allergic reaction to eggs or to a previous flu shot

or

2) Have a history of Guillain-Barré Syndrome (GBS).

Click here to learn more about Guillain-Barré Syndrome (GBS).

If you are sick with a fever when you go to get your flu shot, you should talk to your doctor or nurse about getting your shot at a later date.  However, you can get a flu shot at the same time you have a respiratory illness without fever or if you have another mild illness.

Why get a flu shot? (top)

An annual flu shot is the best way to reduce the chances that you will get the flu.

Influenza is a serious disease, and people of any age can get it.  In an average year, the flu causes 36,000 deaths (mostly among those aged 65 years or older) and 114,000 hospitalizations in the United States.  The "flu season" in the United States is usually from November through April each year.  During this time, flu viruses are circulating in the population.

Why do I need to get a flu shot every year? (top)

Flu viruses change from year to year, which means two things.  First, you can get the flu more than once during your lifetime.  The immunity (natural protection that develops against a disease after a person has had that disease) that is built up from having the flu caused by one virus strain doesn't always hold up when a new strain is circulating.  Second, a vaccine made against one flu virus may not protect against the newer viruses.  That is why the influenza vaccine is updated to include current viruses every year.

A third reason to get a flu vaccine every year is that after you get a flu shot, your immunity to the flu declines over time and may be too low to provide protection after one year.

When should I get a flu shot? (top)

Beginning each September, flu shots should be offered to persons at high risk when they are seen by health-care providers for routine care or as a result of hospitalization.

The best time to get a flu shot, if you are in a high-risk group, is from October through November.  You should avoid getting a flu shot too early, because protection from flu can begin to decline within a few months after getting the shot.  Flu activity in the United States generally peaks between late December and early March.

You can still benefit from getting a flu shot after November, even if flu is present in your community. Vaccine should continue to be offered to unvaccinated persons throughout the flu season as long as vaccine is still available.  Once you get a flu shot, your body makes protective antibodies in about two weeks.

Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP)
Morbidity and Mortality Weekly Report (MMWR), April 12, 2002/ Vol. 51 / No. RR-3.

Does a flu shot work right away? (top)

No. It takes about two weeks after the vaccination for antibodies to develop in the body and provide protection against influenza virus infection.  In the meantime, you are still at risk for getting the flu. That's why it's better to get vaccinated early in the fall, before the flu season really gets under way.

Can I get the flu even though I got a flu shot this year? (top)

Yes. The ability of a flu shot to protect a person depends on two things: 1) the age and health status of the person getting the shot, and 2) the similarity or "match" between the virus strains in the vaccine and those in circulation.  When the "match" between vaccine and circulating strains is close, flu vaccine prevents influenza in about 70%-90% of healthy persons younger than age 65 years. Among elderly persons living outside chronic-care facilities (such as nursing homes) and those persons with long-term (chronic) medical conditions, flu vaccine is 30%-70% effective in preventing hospitalization for pneumonia and influenza. Among elderly nursing home residents, flu vaccine is most effective in preventing severe illness, secondary complications, and deaths related to the flu. In this population, the vaccine can be 50%-60% effective in preventing hospitalization or pneumonia and 80% effective in preventing death from the flu.

Many people think that "the flu" is any illness with fever or cold-like symptoms, or any illness with stomach or intestinal problems, such as vomiting, nausea, or diarrhea.  They may expect flu vaccine to prevent these illnesseses.  But flu shots are effective only against illness caused by flu viruses, and not against other causes of fever, colds, or gastro-intestinal illnesses caused by other viruses.

How are the viruses for flu shots selected? (top)

Each year, many labs throughout the world, including in the United States, collect flu viruses. Some of these flu viruses are sent to one of four World Health Organization (WHO) reference labs, one of which is at the Centers for Disease Control and Prevention (CDC) in Atlanta, for detailed testing.  These laboratories also test how well antibodies made to the current vaccine react to the circulating virus and new flu viruses. This information, along with information about flu activity, is summarized and presented to an advisory committee of the U.S. Food and Drug Administration (FDA) and at a WHO meeting. These meetings result in the selection of three viruses (two subtypes of influenza A viruses and one influenza B virus) to go into flu shots for the following fall and winter. Usually one or two of the three virus strains change in the vaccine each year.

What are the risks from getting a flu shot? (top)

The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot.  The risk of a flu shot causing serious harm, or death, is extremely small.  However, a vaccine, like any medicine, may rarely cause serious problems, such as severe allergic reactions.  Almost all people who get influenza vaccine have no serious problems from it.

What are the side effects that could occur? (top)

• Soreness, redness, or swelling where the shot was given
• Fever (low grade)
• Aches

If these problems occur, they begin soon after the shot and usually last one to two days.

Can severe problems occur? (top)

Life-threatening allergic reactions are very rare. Signs of serious allergic reaction can include breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat, or dizziness.  If they do occur, it is within a few minutes to a few hours after the shot.  These reactions are more likely to occur among persons with a severe allergy to eggs, because the viruses used in the influenza vaccine are grown in hens' eggs.  People who have had a severe reaction to eggs or to a flu shot in the past should not get a flu shot before seeing a physician.

Guillain-Barré Syndrome (top)

Normally, about one person per 100,000 people per year will develop Guillain-Barré syndrome (GBS), an illness characterized by fever, nerve damage, and muscle weakness.  In 1976, about 46 million U.S. residents were vaccinated against swine flu, and 532 of them developed GBS. Thirty-two died. This number of cases was greater than expected and established a link between the swine flu shot and GBS.  Since then, concern has been raised about a possible link between other, non-swine flu vaccines and GBS.

What is GBS? (top)

Guillain-Barré (pronounced ghee-YAN bah-RAY) syndrome is a disease in which the body damages its own nerve cells (outside of the brain and spinal cord), resulting in muscle weakness and sometimes paralysis.  GBS can last for weeks to months and 5 to 6% of people who develop GBS die. Most people eventually recover completely or nearly completely, but some people have permanent nerve damage.  GBS affects people of both sexes and all ages, and has been reported in all races.

What causes GBS? (top)

It is thought that GBS may be triggered by an infection.  The infection that most commonly precedes GBS is caused by a bacterium called Campylobacter jejuni.  Other respiratory or intestinal illnesses and other triggers may also precede an episode of GBS.  In 1976, vaccination with the swine flu vaccine was associated with getting GBS.  Several studies have been done to evaluate if other flu vaccines since 1976 were associated with GBS.  Only one of the studies showed an association.  That study suggested that one person out of 1 million vaccinated persons may be at risk of GBS associated with the vaccine.

More facts about potential side effects of the influenza vaccine can be found in "Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP)."

What should I do if I have had a serious reaction to influenza vaccine? (top)

• Call a doctor, or get to a doctor right away.
• Tell your doctor what happened, the date and time it happened, and when you got the flu shot.
• Ask your doctor, nurse, or health department to file a Vaccine Adverse Event Reporting System (VAERS) form, or call VAERS at 1-800-822-7967.

VAERS website

How can I learn more about influenza vaccine? (top)

• Ask your doctor or nurse.  They can give you the vaccine package insert or suggest other sources of information.
• Call your local or state health department
• Contact the Centers for Disease Control and Prevention (CDC) at:
• 1-800-232-2522 (English)
• 1-800-232-0233 (Español)
• National Immunization Program's website

"Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP)," Morbidity and Mortality Weekly Report (MMWR), April 12, 2002/ Vol. 51 / No. RR-3.

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