Data from the first clinical trials of the H1N1 (swine flu) vaccine in Australia and Britain show that one dose of the vaccine could be just as effective as two, protecting a recipient from the virus within about 10 days . The results are a potential boon, considering concerns that the anticipated supply of vaccine may not be enough to cover all those considered "high-risk", including pregnant women, children and health care workers.

If the results hold true, the number of people who can be vaccinated could be doubled, though two doses may still be needed for young children.

120 of the adults in the trial were given one 15-microgram shot and their blood tested 21 days later. 97 percent of this group responded well, showing enough antibodies for protection from the H1N1 virus. Another group of adults was given double the dose, 30-micrograms, resulting in the same amount of protection.

The Australian vaccine manufacturers, CSL Limited, is contracted to supply the United States with millions of doses of the vaccine; the president of the American branch expects the vaccine to do just as well in trials here. In fact, Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, agrees, saying that trials sponsored by the National Institutes of Health corroborate the Australian trials.

More good news - side effects experienced by approximately half the trial's participants were limited to the normal and mild side effects of the seasonal flu vaccine, including soreness at the injection site and headaches.

The vaccine most likely will not be available until late October. This estimated arrival date may miss the mark, according to a new study. "If the H1N1 flu follows the pattern we are expecting we should see a sizable outbreak in the U.S. starting in early September and probably peaking in mid- to late- October," says Ira Longini, a professor of biostatistics at the University of Washington in Seattle and lead researcher.

However, Longini still recommends getting vaccinated, as swine flu is expected to linger in the population for around 20 years, with more outbreaks predicted this winter and spring and in the years to come.

Have swine flu questions and looking for answers? Explore iVillage's Swine Flu Survival Guide.

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