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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.

Last week, nearly 60% of U.S. doctor visits were for flu-like symptoms, Anne Schuchat, MD, director of the CDC's respiratory disease center, said at the news conference. That means there's as much flu going around now as there was at the peak of last flu season.

"These levels of influenza activity are extremely unusual for this time of year," Schuchat said. "Ninety-eight percent of the viruses are novel H1N1."

Fauci said plans are still on track to start distributing some 45 million doses of swine flu vaccine in mid-October. About 20 million more doses are expected to become available every week after that. The U.S. has purchased 195 million doses in all. That now looks like more than enough to vaccinate every American who wants it.

Vaccine supplies could be extended even further. By giving the vaccine along with an immune-boosting substance called an adjuvant, the Australian studies show, just one half-dose of vaccine works as well as a full dose without adjuvant.

Unfortunately, these adjuvants have not yet been approved by the U.S. FDA. This means they will not be used in the U.S. during this flu season. But adjuvant is approved in Europe and elsewhere, and should greatly extend the worldwide supply of swine flu vaccine.

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