A single low dose of H1N1 vaccine may be enough to protect adults from the flu virus that has been spreading around the world, new data shows.

Researchers in Australia said they tested the H1N1 vaccine in 240 people ages 18 to 64. Half were given a dose of 15 micrograms while the others were given 30 micrograms.

After 21 days, blood samples showed that most participants had an immune response of 1 to 40 titers or more, the researchers said.

Having an immune response of 1 to 40 titers is one of the criteria for the Food and Drug Administration to approve a flu vaccine, according to Dr. Raymond Strikas of the National Vaccine Program, who was not involved with the study, which was published in the New England Journal of Medicine on Thursday.

The researchers report that the 15 milligram dose of the H1N1 vaccine has mild to moderate vaccine-associated reactions, similar to what they see when the seasonal flu vaccine is given.

The National Institutes of Health scientists also have been conducting clinical trials on the H1N1 vaccine in several sites across the country.

(Source: CNN)