The flu virus can change from year to year, and the protection you get from a flu vaccine declines over time. That's why you need a flu vaccination once a year, every year.

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The best time to get vaccinated is in October or November, at the start of the flu season. However, since flu season often does not peak until December or later, you can still benefit from getting the flu vaccine after November.

It takes about two weeks after vaccination for antibodies to develop in the body and protect you against infection from the flu virus - but all is not lost if you can't get your flu vaccine before November.

In recent years, flu activity hasn't peaked until late December through March. Vaccination is recommended throughout the winter months.

For high-risk individuals - children, diabetics, seniors, anyone else who are immune suppressed - the vaccine cuts your risk.

However, it is not a guarantee. The science of predicting which type of flu virus will occur in the US in any given year is not well developed, for two reasons: the flu virus mutates and there are many different flu viruses.

There are two types of flu vaccines. Be sure to talk with your doctor about which is best for you:

1. The flu shot is a trivalent inactivated vaccine (TIV), which contains a killed virus. Some people are skeptics, thinking they might "catch" the flu from a flu shot. Not true. You might still get the flu, but you're not likely to be as sick. Side effects from a flu shot may include a sore arm, fever, and body aches, but they'll be milder than flu symptoms and will last only a day or two.
2. The flu nasal spray, a live influenza vaccine (LAIV), contains a weakened live virus and is for use only among healthy people between ages five and 49.

If you're allergic to eggs, ill with a high fever, or have had a severe reaction to a flu vaccine in the past, ask your doctor whether you should get the flu vaccine.

It takes approximately two weeks for your body to build up the antibodies needed to protect you from the flu. No vaccine is 100 percent effective. You may still get the flu, but you're likely to be far less sick.

For more information about preventing and treating influenza, visit www.cdc.gov/flu