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Do Flu Shots Work?

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Updated September 13, 2013

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Do Flu Shots Work?

Everyone over the age of 6 months should get a flu shot.

Photo courtesy: CDC (PHIL)

How Flu Shots Work:

To determine if flu shots work, you must first know how they work. In simple terms, a killed virus (in the flu shot) or an attenuated and weakened live virus (in the nasal flu vaccine) is introduced into the body, which then develops antibodies to fight it off and provide you with immunity. However, there are countless strains of influenza, and only three are included in the flu vaccine each year. So the vaccine only provides protection against those three that researchers believe are most likely to make people sick.

Types of Influenza:

As mentioned above, the types of flu virus that are circulating and making people sick generally change from year to year. This is why we have to get a new vaccine each flu season.

Flu Shot Basics:

Flu shots are now recommended for everyone over the age of 6 months who wants one. Among the highest at risk for complications from the flu are young children, older adults, those with a weakened immune system or chronic health condition, and pregnant women.

It takes about two weeks after you get the flu vaccine for it to become effective, and protection generally lasts for about 6 months.

Flu Shot Reactions:

Serious side effects from flu shots are very rare, but there are some common ones that you should be aware of. Among the most common are soreness at the injection site and feeling more tired than usual.

Can You Get the Flu From the Flu Shot?:

One of the most common concerns about the flu vaccine is that it can actually give you the flu. It must be frustrating to get sick right after getting the flu shot, but it just isn't scientifically possible to get the flu from the flu vaccine. However, there are several explanations for why you might have become sick after getting the flu vaccine.

Why You Might Get Sick After the Flu Shot:

Instead of blaming your illness on the flu vaccine, learn what could really have made you sick. There is even a possibility that you could have the flu. It takes about two weeks for the vaccine to become effective. That means if you get the flu a day or two after getting the vaccine, you were most likely exposed before you were vaccinated.

The flu vaccine is not guaranteed to work for everyone, but it's your best shot at avoiding the flu.
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