A rooster that has been genetically modified to prevent the spread of bird flu if it is infected with the H5N1 influenza virus. ((Norrie Russell/The Roslin Institute))

Scientists have genetically engineered chickens that can't spread bird flu to their neighbours.

The experiment is a first step in exploring new ways to thwart a type of influenza that experts fear might one day spark a pandemic. But it would take a lot of additional research to see whether the resulting chickens and their eggs would be safe to eat.

A team led by the University of Cambridge bred chickens with a piece of DNA that produces what researchers dubbed a decoy molecule, which tricks and diverts an enzyme key to the reproduction of the flu virus.

Then researchers infected those chickens with bird flu and put them in cages with uninfected chickens. The infected birds still died, but they didn't spread bird flu to the other chickens.

The research was published in Friday's edition of the journal Science.

It's not an approach for wild birds that carry bird flu, but the researchers argue that breeding flu-resistant chickens could be valuable in warding off the deaths of commercial flocks  and might provide more protection against evolving strains than attempts to vaccinate poultry.

Bird flu, known formally as H5N1 influenza, occasionally infects people who have close contact with infected poultry. It is lethal when it does because the infection is so different from typical human influenza strains. The concern is that it might eventually evolve to spread easily among people.