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Cold, Flu, & Cough Health Center

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Swine Flu Shot Gives Fast Protection

H1N1 Swine Flu Vaccine Protects in 8-10 Days, U.S. Trials Confirm
WebMD Health News
Reviewed by Louise Chang, MD

Sept. 11, 2009 - You'll be protected from swine flu eight to 10 days after getting a single shot of the H1N1 swine flu vaccine -- at least if you're a healthy adult, U.S. studies show.

Results of studies in children, who may still need two doses of the swine flu vaccine, won't be available for two weeks. And it's still unclear whether adults with chronic health conditions might need two shots of the pandemic flu vaccine.

Swine Flu Outbreak: Get the Facts

Swine Flu Slideshow

Learn more about the H1N1 swine flu and see what you can do to stay healthy.

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But the findings in adults amaze and delight health officials. The early U.S. study results confirm yesterday's report from Australian studies that adults need only one standard dose of H1N1 swine flu vaccine.

"Americans who get the H1N1 vaccine most likely will be protected sooner than we thought," HHS Secretary Kathleen Sebelius said at a news conference held to announce the findings. "Now it appears most people have a robust immune response in eight to 10 days. It shortens the window of worry, and more people can be protected much earlier."

The speedy immune response was so unexpected that researchers didn't even bother to look for it in many clinical trial subjects. Some of the U.S. trials didn't test for swine flu-neutralizing antibodies until 21 days after the first shot. Fortunately, enough of them did.

Also surprising is how well the swine flu vaccine worked in the U.S. studies. The H1N1 vaccines made by CSL and Sanofi raised protective levels of antibody in 80% to 96% of adults aged 18 to 64 and in 50% to 60% of those over age 65.

"This is very good news for the H1N1 vaccine program," Anthony Fauci, MD, director, of the U.S. National Institute of Allergy and Infectious Diseases, said at the news conference. "There have been no significant adverse events whatsoever. The vaccine is very well tolerated."

Swine Flu Race Is On

Now the race is on to get the swine flu vaccine into people's arms -- or noses, as a FluMist inhaled version of the vaccine will be available. Swine flu is now widespread in 11 states; all 50 states report cases.

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