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What Everyone Should Know About Flu and the Flu Vaccine
October 6, 2004

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What is Flu?

The flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. The best way to prevent the flu is to get a flu vaccine each fall.

Every year in the United States, on average:

Some people are at high risk for serious flu complications, such as older people, young children, and people with certain health conditions, including pregnancy.

Symptoms & Complications of Flu

Symptoms of flu include:

  • fever (usually high),
  • headache,
  • extreme tiredness,
  • dry cough,
  • sore throat,
  • runny or stuffy nose, and
  • muscle aches.
  • Gastro-intestinal symptoms, such as nausea, vomiting, and diarrhea, are much more common among children than adults.

Some of the complications caused by flu include bacterial pneumonia, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. Children may get sinus problems and ear infections.

How Flu Spreads

The flu spreads in respiratory droplets caused by coughing and sneezing. It usually spreads from person to person, though occasionally a person may become infected by touching something with virus on it and then touching their mouth or nose.

Adults may be able to infect others beginning 1 day before getting symptoms and up to 7 days after getting sick. That means that you can give someone the flu before you know you’re sick as well as while you are sick.

Preventing the Flu

The single best way to prevent the flu is to get a flu vaccine each fall. There also are certain good health habits that can help prevent the flu (see below). In addition, antiviral medications may be used to prevent the flu. (For more information, see Antiviral Drugs and the Flu.)

Flu Vaccine

There are two types of vaccines:

  • The "flu shot" -- an inactivated vaccine (containing killed virus) that is given with a needle. The flu shot is approved for use in people older than 6 months, including healthy people and people with chronic medical conditions.
  • The nasal-spray flu vaccine -- a vaccine made with live, weakened flu viruses that do not cause the flu (sometimes called LAIV for “Live Attenuated Influenza Vaccine”). LAIV is approved for use in healthy people 5 years to 49 years of age who are not pregnant.

About two weeks after vaccination, antibodies that provide protection against influenza virus infection develop in the body.

When to Get Vaccinated

October or November is the best time to get vaccinated, but you can still get vaccinated in December and later. Flu season can begin as early as October and last as late as May.

Who Should Get Vaccinated?

Because of a shortfall in flu shot production for this season, CDC is recommending that certain people be given priority for getting the flu shot. People in the following groups should seek vaccination this season:

  • all children aged 6–23 months;
  • adults aged 65 years and older;
  • persons aged 2–64 years with underlying chronic medical conditions;
  • all women who will be pregnant during the influenza season;
  • residents of nursing homes and long-term care facilities;
  • children aged 6 months–18 years on chronic aspirin therapy;
  • health-care workers involved in direct patient care; and
  • out-of-home caregivers and household contacts of children aged <6 months.

These are people who are at high risk for serious flu complications or are in contact with people at high risk for serious flu complications.

People who are not included in one of the priority groups listed above are asked to forego or defer vaccination because of the vaccine supply situation.

Who Should Not Be Vaccinated

There are some people who should not be vaccinated. These include:

  • People who have a severe allergy to chicken eggs.
  • People who have had a severe reaction to an influenza vaccination in the past.
  • People who developed Guillain-Barré syndrome (GBS) within 6 weeks of getting an influenza vaccine previously.
  • Children less than 6 months of age.
  • People who are sick with a fever. (These people can get vaccinated once their symptoms lessen.)

Other Good Health Habits

  • Avoid close contact.
    Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.
  • Stay home when you are sick.
    If possible, stay home from work, school, and errands when you are sick. You will help prevent others from catching your illness.
  • Cover your mouth and nose.
    Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick.
  • Clean your hands.
    Washing your hands often will help protect you from germs.
  • Avoid touching your eyes, nose or mouth.
    Germs are often spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.

See Also...


Safer, Healthier People

Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA 30333, U.S.A
Tel: 404-639-3311 / Flu Public Inquiries: 800-232-2522 • español 800-232-0233 • TTY 800-243-7889
Clinician Information Line: 877-554-4625