"Generating broadly neutralising antibodies to multiple strains of influenza in animals through vaccination is an important milestone in the quest for a universal influenza vaccine," said Dr Anthony S. Fauci, NIAID director.

"This significant advance lays the groundwork for the development of a vaccine to provide long-lasting protection against any strain of influenza."

"A durable and effective universal influenza vaccine would have enormous ramifications for the control of influenza, a disease that claims an estimated 250,000 to 500,000 lives annually, including an average of 36,000 in the United States."

Dr Gary J. Nabel of NIAID and his colleagues first primed mice, ferret and monkey immune systems with a vaccine made from DNA encoding the influenza virus hemagglutinin (HA) surface protein.

After being primed with the DNA vaccine, the mice and ferrets received a booster dose of the 2006-2007 seasonal influenza vaccine or a vaccine made from a weakened cold adenovirus containing HA flu protein.

Monkeys were boosted with the seasonal flu vaccine only.

The prime-boost vaccine stimulated an immune response to the stem of the lollipop-shaped hemagglutinin of influenza virus.

Unlike HA's head -- which mutates readily, allowing the virus to become unrecognisable to antibodies -- the stem varies relatively little from strain to strain.

In principle, antibodies generated against the stem of HA should be able to recognise and neutralise multiple flu strains.

"We are excited by these results," said Dr Nabel.

"The prime-boost approach opens a new door to vaccinations for influenza that would be similar to vaccination against such diseases as hepatitis, where we vaccinate early in life and then boost immunity through occasional, additional inoculations in adulthood."