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Influenza vaccine (flu shot)

June 10, 2008 - 7:30am
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Influenza vaccine (flu shot)

Influenza, also known as the “flu,” is a potentially serious disease caused by a virus. The virus spreads from infected persons to the nose or throat of others causes influenza. In the United States, the “flu season" is from November through April each year.

Influenza can cause:

  • Fever
  • Sore throat
  • Cough
  • Headache
  • Chills
  • Muscle aches

People of any age can get influenza. Most people experience the effects of influenza for only a few days, but some get much sicker and may need to be hospitalized. Influenza causes thousands of deaths each year. These deaths occur mostly among the elderly.

Influenza vaccine can prevent influenza.

The viruses that cause influenza change often. For this reason, the influenza vaccine is updated each year to include the current viruses. It takes about 2 weeks after getting the shot for antibodies to develop in your body and provide protection again influenza virus infection. Protection may last up to a year.

Who should get influenza vaccine

People at risk for getting a serious case of influenza or influenza complications, and people in close contact with them (including all household members) should get the vaccine. An annual flu shot is recommended for these groups:

  • Everyone 50 years of age or older
  • Residents of long term care facilities housing persons with chronic medical conditions.
  • Adults and children who have a serious long-term health problem such as:
    • Heart disease
    • Kidney disease
    • Lung disease
    • Metabolic disease, such as diabetes
    • Asthma
    • Anemia, and other blood disorders
  • Anyone whose immune system is weakened as a result of:
    • HIV/AIDS or other diseases that affect the immune system
    • Long-term treatment with drugs such as steroids
    • Cancer treatment with x-rays or drugs
  • Anyone 6 months to 18 years of age on long-term aspirin treatment (who could develop Reye Syndrome if they catch influenza)
  • Women who will be past the 3rd month of pregnancy during the influenza season
  • Doctors, nurses, hospital employees, family members, or anyone else coming in close contact with people at risk of serious influenza

Others who should consider getting influenza vaccine:

  • People involved in essential community services
  • People traveling to the Southern hemisphere between April and September, or to the tropics at any time
  • People living in crowded conditions, such as dormitories
  • Anyone who wants to reduce his or her risk of catching influenza

When to get influenza vaccine

Influenza can start spreading as early as December. Therefore, the best time to get influenza vaccine is during October and November. However, getting the vaccine after November can still provide protection. A new shot is needed each year.


People 9 years of age and older need one shot.

Children less than 9 years old need two shots, given one month apart, the first time they get vaccinated against influenza.

Influenza vaccine can be given at the same time as other vaccines, including pneumococcal vaccine.


In spite of having the influenza vaccine, some people still get influenza. Influenza viruses change often, and the vaccine might not always cover them. But vaccinated people who do get influenza often have a milder case than people who did not get the shot.

Many people with fever and cold symptoms think they have influenza. They may believe that the vaccine is supposed to protect them from these illnesses as well. But influenza vaccine is effective only against illness caused by influenza viruses, and not against other illnesses.

When not to get influenza vaccine

Talk with your doctor before getting an influenza vaccination if you:

  • Have a severe allergy to hens’ eggs
  • Have had a severe reaction to an influenza vaccine in the past
  • Have developed Guillain-Barré Syndrome (GBS) in the 6 weeks after getting the influenza vaccine

If you have a fever or a severe illness, you should usually wait until you recover before getting influenza vaccine. Ask your doctor or nurse about rescheduling the vaccination.

Risks associated with influenza vaccine

A vaccine, like any medicine, is capable of causing serious problems, such as severe allergic reactions. The risk of a vaccine causing serious harm, or death, is extremely small. Almost all people who get influenza vaccine have no serious problems from it. The viruses in the vaccine are killed, so you cannot get influenza from the vaccine.

Mild problems

  • Soreness, redness, or swelling in the area of the vaccine
  • Fever
  • Aches

If these problems occur, they usually begin soon after the shot and last 1-2 days.

Severe problems

Life-threatening allergic reactions are very rare. If they do occur, it is within a few minutes to a few hours after the shot. Signs of serious allergic reaction include breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat or dizziness.

In 1976, swine flu vaccine was associated with a severe paralytic illness called Guillain-Barr‚ Syndrome (GBS). Influenza vaccines since then have not been clearly linked to GBS.

If there is a risk of GBS from current influenza vaccines, it is estimated to be very small(between 1 or 2 cases per million persons vaccinated. This is much less risk than the risk of severe influenza, which can be prevented by vaccination.

If there is a moderate or severe reaction

Be alert for any unusual condition, such as a high fever or behavior changes. Signs of a serious allergic reaction can include difficulty breathing, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat or dizziness.

What you should do

If a severe reaction occurs, call a doctor, or get the person to a doctor right away.

Tell your doctor what happened, the date and time it happened, and when the vaccination was given. 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.


Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.



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