In clinical trials, the new drug not only required fewer scarce antigens, it also triggered a far more effective immune response, according to the study, published in the British journal The Lancet.
The new drug -- which combines a standard vaccine with a patented oil-in-water emulsion -- produced up to six times as many antibodies capable of neutralising the bird flu virus as the same dose without the emulsion.
Even in weaker doses the drug, produced by GlaxoSmithKline, which also funded the study, proved highly effective.
"The number of pandemic vaccine doses can be stretched 20-25 fold," commented two virologists in The Lancet, Suryaprakash Sambhara of the Centers for Disease Control and Prevention in Atlanta, and Gregory Poland of the May Vaccine Research Group in Rochester, Minnesota.
The highly pathogenic strain of influenza known as H5N1 has caused widespread outbreaks in birds -- especially in Asia, Europe and Africa -- over the last decade, as well as oft-lethal infections in humans.
The human body does a poor job of producing antibodies to defend itself against the virus, especially haemagglutinin H5.
Of 318 laboratory-confirmed cases reported by the World Health Organisation, 192 have been fatal, a staggering 60 percent mortality rate.
Scientists fear that the virus strain could mutate into a form easily transmissible among humans. To date, almost all of those who contracted the disease were in close contacted with infected poultry.
The world's drug makers are already unable to meet demand for a standard seasonal flu vaccine. In the event of a pandemic of an especially virulent strain -- such as the flu that left 50 million dead nearly a century ago -- it would be impossible under current conditions to produce enough vaccines.
Moreover, because most people have never been exposed to H5N1 -- making them "immunologically naive," in the jargon of virologists -- a single dose of vaccine would probably prove inadequate.
In the study, researcher Geert Leroux-Roels of the Center for Vaccinology at Ghent University in Belgium gave four antigen doses ranging from 3.8 micrograms to 30 micrograms to 400 adults, aged 18-60, divided into eight groups of 50.
Four groups received doses with the oil-water emulsion, and four groups without.
Even at the lowest dose of 3.8 micrograms, the adjuvanted drugs produced up to twice as many antibodies as the 30 microgram doses without the added solution.