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 or a stuffy nose, headache, muscle aches and tiredness. Some people describe the flu as the worst cold of their life. If you get the flu, you should feel better after one or two weeks. But in some people, the flu leads to serious, even life-threatening diseases, like pneumonia. Some people are more likely to get the serious complications. A vaccine (the flu shot) is recommended for these high-risk people to protect them from the flu.

Who is at higher risk?

You have a higher risk of flu complications if you:

• Are 50 years of age 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 risk groups, you should get the flu vaccine every year.

Even some low-risk people should get the vaccine because they might spread the flu to high-risk people. You should get the vaccine if you're a health care worker or if you live (or work) in a long-term care facility. And even if you're 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?

The flu vaccine is a shot. It contains killed viruses. You can't get the flu from the vaccine because the viruses are dead. Instead, the vaccine protects you from the flu. When a “live” virus shows up, your defenses are ready. These defenses keep you from getting the flu. Because flu viruses change from year to year, you must get the shot each year to be protected.

When should I get the vaccine?

You should get the vaccine at the beginning of the flu season, sometime in October or November. You can get the shot later in the year than November, but because flu season usually begins in the winter months, it would be best to be protected before that time. Sometimes you can get the vaccine in September if it's available.

If I get a flu shot, can I still get the flu?

Yes. Even with a flu shot, you aren't 100 percent protected. Each year, the flu vaccine contains three different strains (kinds) of the virus. The strains chosen are those that scientists believe are the strains most likely to show up in the United States that year. If the choice is right, the vaccine is 70 to 90 percent effective in preventing the flu in healthy people under 65 years of age. If you're older than 65, the vaccine is less likely to prevent the flu. Even if you get the flu after the vaccine, your flu symptoms should be milder than if you didn't get the vaccine. You'll also be less likely to get complications from the flu.

Is the vaccine safe?

Yes. The flu vaccine is safe for all age groups over six months of age. There are very few side effects too. Your arm may be sore for a few days. You may have a fever, feel tired or have sore muscles for a short time.

A few people are allergic to the flu vaccine. If you have a severe allergy to eggs, you shouldn't get the shot. You should tell your doctor about your egg allergy. He or she will tell you if it's okay to get the flu shot.

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)