By James S. Winshall, M.D.
Brigham and Women's Hospital

As the days shorten and the weather cools, it’s once again time to start thinking about the influenza or “flu” vaccine. Although many people are distracted by the threat of SARS or West Nile virus, it’s important to keep in mind that influenza kills an estimated 20,000 Americans every year. Getting vaccinated for influenza may be one of the best ways to stay healthy this winter.

The following are some frequently asked questions about the influenza vaccine.

Who should get vaccinated?

Anybody who wants to reduce their chance of contracting influenza. Although the top priority is to vaccinate those at high risk of the disease and its complications, even young, healthy people who get influenza can become quite ill. Influenza vaccine appears to benefit almost everyone, regardless of age or health. Getting the influenza vaccine may help to keep you healthy, and thereby able to take care of your family and avoid missed days from work.

The influenza vaccine is highly recommended for the following high risk groups:

The vaccine is also recommended for the following people:

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Who should not get vaccinated?

If you are scheduled to receive the vaccine but develop a fever or serious illness, talk to your health-care provider about delaying the vaccine until you recover.

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I never get sick. Why should I be vaccinated?

Anyone can get influenza, even those who are usually very healthy. The typical case of influenza will cause several days of severe symptoms including high fever, muscle aches, cough and fatigue. Most people will spend the time out of work and in bed.

In the elderly, the very young and in those with underlying medical problems, influenza can cause a life-threatening illness that often requires hospitalization and a prolonged recovery period.

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When should I get vaccinated?

In most parts of the United States, influenza season starts no earlier than mid-November and may last until April. Since it takes a little while for your body to respond to the vaccine, the best time for vaccination is during the months of October and November. If you are delayed until December or even January, it is still worthwhile being vaccinated since this may protect you from a late outbreak of influenza.

Since there is plenty of flu vaccine available this year, there is no need to delay your vaccine if you are not in the highest risk group.

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Do I need to be vaccinated every year?

Yes. The vaccine changes slightly each year to provide coverage for those strains of influenza that are most likely to affect the United States. Furthermore, each dose of vaccine provides protection against influenza for only about six months.

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Can I get influenza from the vaccine?

No. The vaccine is made from killed viruses, which cannot cause infection. Some people have minor aches and chills after the vaccine, but this should not be confused with influenza itself.

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Last year I was vaccinated but still got the flu. Why?

The vaccine does not provide 100-percent protection against influenza. However, those who have been exposed to influenza but have been vaccinated are still less likely to develop serious symptoms.

It’s also important to remember that influenza is different from many other viruses that cause flulike illnesses, such as the common cold. The influenza vaccine does not provide protection against these other viruses.

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Are there any serious side effects from the flu vaccine?

Major side effects from the influenza vaccine are very rare. Occasionally, people will have an allergic reaction to the vaccine, but it is uncommon for this to cause serious harm or death. Allergic reactions usually develop within minutes to hours of receiving the vaccine.

There is also evidence that a batch of swine-flu vaccine in the 1970s caused a serious neurological illness known as Guillain-Barré syndrome, However, this has not been a problem with more recent batches of vaccine.

Minor reactions to the influenza vaccine may include:

These symptoms usually start a day or two after receiving the vaccine and should go away within a couple of days.

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What about the new nasal-spray form of the flu vaccine?

This year a new type of influenza vaccine will be available. FluMist is a live form of the virus that is sprayed into the nose, thereby avoiding the needle jab required with the usual flu shot. It appears to protect against influenza, but perhaps not as well as the injection. So far, the U.S. Food and Drug Administration has approved FluMist only for use in healthy people between the ages of 5 and 50. That means that almost all people at high risk of influenza should still receive the usual influenza shot.

FluMist is also more expensive than the usual flu shot and requires special handling.

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I am allergic to eggs and cannot get the flu vaccine. Are there alternative treatments that can prevent influenza?

There is no alternative, egg-free vaccine to prevent influenza. However, if you have not been vaccinated and are exposed to influenza, several medications may lessen or prevent symptoms. These medications include amantadine, rimantadine (Flumadine), oseltamivir (Tamiflu), and zanamivir (Relenza). If you find yourself in this situation, talk to your doctor immediately, since the medications must be taken promptly to be effective.

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I am six months pregnant. Should I be vaccinated?

Absolutely. Influenza can cause serious illness in pregnant women, especially during the later stages of pregnancy. Women who will be beyond their third month of pregnancy during flu season are a top priority for vaccination.

There is no evidence that influenza vaccine can cause miscarriage or other problems during any stage of pregnancy. However, some doctors prefer to wait until the fourth month or beyond to vaccinate pregnant women.

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Will the flu vaccine protect me from SARS?

Unfortunately, no. However, some experts have suggested that getting vaccinated against the flu may help to prevent an illness that could be mistaken for SARS.

To learn more about influenza vaccine, visit the CDC Web site.

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James S. Winshall, M.D., is an associate physician at Brigham and Women's Hospital. In addition to his role as senior editor at Harvard Health Publications, Dr. Winshall practices general internal medicine and is an assistant professor at Harvard Medical School.