Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 2004;69(2):379-380

What is influenza?

Influenza (also called the flu) is a viral infection in the nose, throat, and lungs. About 10 to 20 percent of Americans get the flu each year. Some people get very sick. Each year, about 130,000 people go to a hospital with the flu, and 20,000 people die because of the flu and complications.

The flu may cause fever, cough, sore throat, a runny nose or a stuffy nose, headache, muscle aches, and tiredness. Some people describe the flu as being like the worst cold of their life. Most people feel better after one or two weeks, but for some people, the flu leads to serious, even life-threatening diseases, such as pneumonia. Influenza vaccine (the flu shot) is recommended for people who are more likely to get really sick and need to be protected from getting the flu.

Who is at higher risk?

You have a higher risk of flu complications like pneumonia if you:

  • Are 50 years or older

  • Are a health care worker

  • Have a lung problem, such as asthma or emphysema

  • Have a suppressed immune system

  • Have a problem with your kidneys

  • Have diabetes, heart disease, or other long-term health problems

If you are in any of these groups, you should probably get the flu vaccine every year.

Other people also should get the vaccine because they might spread the flu to high-risk people. You should get the vaccine if you work in a long-term care facility. Even if you are not at higher risk, you may want to get the flu vaccine so you don't get sick with the flu.

What is the flu vaccine?

There are two kinds of flu vaccine. The first kind is a shot that contains killed viruses. You can't get the flu from the shot because the viruses are dead. Your body builds up antibodies to the virus to protect you from the flu. When a “live” virus shows up, your defenses are ready. These defenses keep you from getting the flu.

The second kind is a liquid that you spray up your nose (a nasal mist). The nasal mist contains live viruses. These viruses have been changed so they do not grow well at body temperature, but cause your body to build up antibodies to the actual flu virus. Only healthy people five to 49 years of age can use the nasal mist.

Because flu viruses change from year to year, you must get the shot or use the nasal mist each year to be protected.

If I get a flu shot or use the nasal mist, can I still get the flu?

Yes. Even with a flu shot or the nasal mist, you aren't completely protected. Each year, the flu vaccine contains three different strains (kinds) of the virus. The strains chosen are those that scientists believe are most likely to show up in the United States that year. If their choice is right, the vaccine is 70 to 90 percent effective in preventing the flu in healthy people younger than 65 years. If you're older than 65, the vaccine is less likely to prevent the flu. If you get the flu after the vaccine, however, your flu symptoms should be milder than if you didn't get the vaccine. You also will be less likely to get complications from the flu.

Is the vaccine safe?

Yes. The flu shot is safe for people older than six months. The shot has few side effects. Your arm may be sore for a few days. You may have a fever, feel tired, or have sore muscles for a short time.

The nasal mist is safe for people older than five years. However, people who have asthma or other airway diseases, and immune deficiency diseases or immunosuppression should not use the nasal mist. The nasal mist has a few side effects, including runny nose, nasal congestion, sore throat, and cough.

Some people are allergic to the flu vaccine. If you have a severe allergy to eggs, you shouldn't get the shot or use the nasal mist. You should talk to your doctor about your egg allergy. He or she will tell you if it is okay for you to get a flu vaccine.

Some pregnant women should not get a flu vaccine. Talk to your doctor if you are pregnant and want to get a flu vaccine.

Where can I learn more about the flu shot?

For more information, you can call the Centers for Disease Control and Prevention's National Immunization Information Hotline at these numbers:

  • 1-800-232-2522 (English)

  • 1-800-232-0233 (Spanish)

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Copyright © 2004 by the American Academy of Family Physicians.

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