Researchers have developed gene-edited chickens that are partially resistant to bird flu.
Although the birds are not completely immune, the scientists say their work shows it might be possible to block the virus in three years.
The latest results suggest that making further changes to the birds' DNA could produce fully immune chickens.
The researchers identified three genes they believed were important for the bird flu (formally known as avian influenza) virus to reproduce in the chickens. They made two small changes to one of the genes using a technique known as gene editing.
The resulting chickens had no side effects after two years. They also had increased resistance to bird flu, but were not fully immune: half the chickens infected with a high dose of the virus developed an infection.
Prof Mike McGrew told BBC News that experiments in test tubes showed if changes are made to all three genes, then a fully resistant bird might be possible.
Bird flu is a major global threat, with a devastating impact in both farmed and wild bird populations. In the UK alone, the current outbreak of H5N1 bird flu has decimated seabird populations and cost the poultry industry more than £100 million in losses.