Just one dose of vaccine may be enough to protect adults against H1N1 influenza, according to preliminary findings of a study underway in Australia.

A single 15 microgram dose produced “a robust immune response” in a majority of healthy adults tested, according to the study conducted by researchers at Australian vaccine manufacturer CSL and published in the New England Journal of Medicine.

Later today, US health officials are expected to release preliminary findings of similar studies underway in this country, which corroborate the Australian study and suggest a single dose of H1N1 vaccine produces a proper immune response in adults within eight to ten days.

These studies would suggest H1N1 vaccine will be available to more people, since previous assumptions were that each person would require two separate doses.

The Centers for Disease Control and Prevention anticipates 195-million doses of vaccine will become available in the US by the end of the year. Federal health officials estimate 159-million people are at highest risk for getting the disease or suffering complications, including pregnant women, children, people with chronic medical conditions, health care workers and people caring for infants.

A single dose would also simplify logistics, reduce costs and eliminate the three week wait time between vaccinations that was expected in a two dose regimen.

Because the initial studies involved adults, the proper dosage for children remains under investigation.

However, researchers believe children under 9 years of age may still require two doses of H1N1 vaccine, just as they require two doses the first time they are vaccinated against seasonal flu. Kids require the additional flu shot since their immune systems have had little or no exposure to influenza viruses.

As for seasonal flu vaccine, a new study published in the New England Journal of Medicine by researchers at the Centers for Disease Control and Prevention suggests this year’s seasonal flu vaccine offers little or no crossover protection against H1N1.

This would suggest Americans wanting to protect themselves from influenza this fall will require the seasonal flu shot — which is already available — AND an H1N1 vaccination — which is expected to become available in mid-October. For more on how the vaccine will be distributed, click here.