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Flu Shots

What are flu shots?

Flu shots can help keep you from getting the flu (influenza). For most people flu infection is uncomfortable and can cause you to miss days at work or school. For some people flu can become a serious illness, even a life-threatening one.

Flu viruses are always present somewhere in the world. In the US flu outbreaks usually happen every year between October and March.

Flu causes a coldlike upper respiratory infection. Unlike most colds, however, the flu often causes fever, muscle aches, and dizziness. It can also lead to more serious infections, such as pneumonia. Complications from flu cause up to 36,000 deaths per year in the US. These deaths usually occur among older adults and people who have chronic health problems, such as heart disease and severe asthma.

How do they work?

The formula for the flu vaccine is changed every year according to the recommendations of scientists from the Centers for Disease Control (CDC). They predict which strains of flu virus are most likely to appear the next winter.

The virus in the flu vaccine given as a shot has been inactivated, or "killed." This means you cannot catch the flu from getting a shot. Getting the shot introduces part of the inactive flu virus to your immune system. Your body then reacts by making protective antibodies against the virus.

How effective are they?

Flu shots are usually about 70% effective in preventing flu. Even if you do get the flu, the vaccine helps protect against severe and possibly life-threatening infection. For this reason it is said that the flu shot protects against death from the flu more than from flu itself.

Who should get the flu vaccine?

Everyone 6 months of age and older should get vaccinated against the flu. It is especially important for people at high risk of serious flu complications to get the vaccine. This includes:

  • young children
  • pregnant women
  • people with chronic health problems, like asthma, diabetes, or heart and lung disease, and
  • people 65 years old and older

Vaccination also is important for healthcare workers, and other people who live with or care for high risk people, to keep from spreading flu to high risk people.

Normally, women who are pregnant should get the shot after 13 weeks of pregnancy. However, if they have other chronic medical problems, it is OK to get the shot earlier in the pregnancy.

Who should not get the flu vaccine?

Talk with your healthcare provider before getting a flu shot if you:

  • are sick with a fever
  • have ever had a severe allergic reaction to eggs or to a previous flu shot (eggs are used in the process for making flu vaccine)
  • had Guillain-Barré syndrome (GBS) within 6 weeks after getting the flu vaccine

It is OK to get the vaccine if you just have an upper respiratory infection—that is, a cold—without a fever.

Thimerosal is a preservative used in contact lens solutions and some flu vaccines. Thimerosal-free vaccine is available for people who have allergies or concerns about the preservative.

How is the flu vaccine given?

When you get a flu shot you are injected in the arm with the flu vaccine.

A nasal spray called FluMist is another way to get the flu vaccine. You can be given this nasal spray if you are healthy, age 2 through 49 years, and not pregnant. As with flu shots, you will need a new dose of FluMist every year. Unlike the shot, FluMist is a live virus vaccine. For this reason pregnant women, children under 2 years, and people with weakened immune systems, asthma, or some other medical conditions cannot take the nasal spray.

When should I get the flu vaccine?

The flu vaccine starts being effective 1 to 2 weeks after you get the shot. It is best to get the flu shot in October of each year, before the flu season begins. Try to get the shot no later than November, if possible.

Flu seasons can vary from region to region and continent to continent. If you are at high risk for infection and plan to travel to an area where you might be exposed to the flu, make sure you have an up-to-date flu shot before you go on your trip.

What are the side effects?

For people who do not have egg or thimerosal allergies, the flu vaccine has infrequent, minor side effects, such as:

  • soreness, redness, or swelling where the shot was given
  • mild fever
  • aches

If these problems occur, they start soon after the shot. They may last 1 to 2 days.

Signs of a serious allergic reaction can include breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat, or dizziness. An allergic reaction may occur within a few minutes to a few hours after the shot. If you are having trouble breathing or throat swelling, call 911.

If you think you are having a reaction to the flu vaccine, call your healthcare provider right away. Tell them when you received the vaccine and what your symptoms are. Ask if your provider needs to see you.

Developed by RelayHealth.
Published by RelayHealth.
Last modified: 2011-02-10
Last reviewed: 2010-07-06
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
© 2011 RelayHealth and/or its affiliates. All rights reserved.
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