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Cold, Flu, & Cough Health Center

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Flu Shot: The Vaccine and Its Side Effects

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A simple vaccine is the best way to protect yourself from the flu. It may sound like a minor illness, but it can cause big problems for some people. It can even be deadly.

Learn the facts about the vaccine so you and your family can stay flu-free.

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When Should I Get It?

Peak flu season can start as early as October and run through May. The best time to get a flu shot is as soon as it’s available, usually in September or October. It takes about 2 weeks for the vaccine to take effect. You can still get a shot in December or later, but the earlier you get it, the higher your odds of staying well.

What Types of Vaccine Can I Get?

There are several:

  • The traditional flu shot is an injection into your arm muscle. It’s made from pieces of flu viruses.
  • An egg-free flu shot, unlike other types, isn’t grown inside eggs. It’s an option for people who have egg allergies.
  • The high-dose flu shot is for people ages 65 and older. They may need a stronger dose to get the same protection.
  • An intradermal flu shot uses a tiny needle that only goes skin deep. It’s for people ages 18 to 64.
  • The nasal spray flu vaccine (FluMist) doesn’t use a needle. It’s made from live but weakened flu viruses. Another name for it is LAIV (live attenuated influenza vaccine). It’s for healthy people ages 2 to 49 who aren’t pregnant and who don’t have weak immune systems. Check with your doctor to make sure it’s right for you.

Some vaccines protect against more than one flu virus strain. Trivalent vaccines work against three strains; quadrivalent vaccines fight four types of flu. The traditional flu shot comes in both forms. High-dose and intradermal shots come only in the trivalent form. The nasal spray flu vaccine only comes in the quadrivalent form.

How Does It Work?

The shots and the nasal spray prompt your body to get ready to fight an infection from the flu virus. It helps you create tools, called antibodies, to fight the virus when you’re exposed to it.

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