Researchers at the University of Pennsylvania School of Medicine said they used vaccine via DNA constructed to build antigens against flu, along with a tiny electric pulse, to immunize experimental animals against various strains of the bird-flu virus.

That approach, the scientists said, could allow the build up of vaccine reserves that could be easily and effectively dispensed in case of an epidemic.

"This is the first study to show that a single DNA vaccine can induce protection against strains of pandemic flu in many animal models, including primates," said Professor David Weiner. "With this type of vaccine, we can generate a single construct of a pandemic flu vaccine that will give much broader protection."

The study appeared in the online journal PLoS One.