A new way to vaccinate against avian influenza that tricks the immune system into mounting a broad response against multiple strains of the disease, including strains to which the immune system was never exposed, has been devised by researchers at the University of Pennsylvania School of Medicine.

In the experiments, vaccinated macaques, mice and ferrets were protected from both disease and death when exposed to avian flu.

If proven in humans, this research could lead the way to effectively prepare against an outbreak of pandemic avian flu.

Health officials around the world worry that the H5N1 bird flu virus will mutate into a form that is readly transmitted from person to person, starting an influenza pandemic.

In the latest bird flu outbreak which began in 2003, human cases of H5N1 bird flu have been documented in 15 countries. Data compiled by the World Health Organization shows 385 cases have occurred, and of these, 243 people have died.

The new vaccination method delivers the vaccine via synthetic DNA, or deoxyribonucleic acid, the hereditary material that contains the genetic instructions for the development and functioning of all known living beings.

Traditional vaccines expose a formulation of a specific strain of flu to the body so it can create immune responses against that specific strain.

But a DNA vaccine becomes part of the cell, giving it the blueprint it needs to build antigens that can induce responses targeting diverse strains of pandemic flu.

Because these synthetic DNA vaccines are effective against multiple cross strains, vaccines could be created and stockpiled, prior to a pandemic, and thus be delivered quickly in the event of an outbreak, say the researchers.

"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," says David Weiner, PhD, professor of pathology and laboratory medicine at the university.

"With this type of vaccine, we can generate a single construct of a pandemic flu vaccine that will give much broader protection," he said.

Avian flu is tricky, Weiner said. Not only is it deadly, but it mutates quickly, generating different strains that escape an immune response targeted against one single strain.

Preparing effective vaccines for pandemic flu in advance with either live or killed viruses, which protect against only one or few cross-strains, is therefore very difficult.

How to predict which strain of avian flu may appear at any time is difficult. "We are always behind in creating a vaccine that can effectively protect against that specific strain," notes Weiner.

Influenza viruses are normally highly species-specific, meaning that viruses that infect an individual species - humans, certain species of birds, pigs, horses, and seals - stay “true” to that species, and only rarely spill over to cause infection in other species, according to the World Health Organization, WHO. The one exception is the highly pathogenic H5N1 bird flu virus.