What is an influenza vaccine?

Flu vaccines are the first and best protection against influenza. While flu vaccines are available in the form of a shot or a nasal spray, there are some differences in the groups recommended for each. The regular flu shot is FDA licensed for use in all people 6 months of age and older, including pregnant women. The intradermal flu shot, which uses a 90% smaller needle than the regular flu shot and is injected into the skin instead of the muscle, is FDA licensed for use in adults 18 through 64 years of age. A high-dose flu shot is FDA-licensed specifically for use in people 65 years of age and older. The nasal spray vaccine, also known as the “live attenuated influenza vaccine” or “LAIV,” is FDA licensed for healthy people 2 through 49 years of age, who are not pregnant and who do not have certain health conditions.

While there are many different flu viruses, the flu vaccine protects against the three viruses that research suggests will be most common. The 2011-2012 flu vaccine will protect against an influenza A (H1N1) virus, an influenza A (H3N2) virus and an influenza B virus.

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Influenza vaccine is a drug that makes the immune system develop immunity to the influenza virus to prevent the infection called "the flu." There are many different types and strains of influenza virus that cause infection in humans. Every year scientists around the world use international influenza surveillance data to predict the most likely strains that will cause problems during the following year. The predicted strains are developed into a combination vaccine that is different each year. This seasonal flu vaccine is available as an injection, often called "the flu shot," and as a nasal spray.

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