More than 150 million birds have been killed by various strains of avian flu, according to the World Health Organization. Outbreaks in Asia and Europe have only been contained by wiping out poultry flocks. Various vaccines to date have proven ineffective or difficult to administer. But now two independent groups of researchers have shown that incorporating the proteins of various strains of bird flu into an existing virus vaccine can yield effective protection for birds.

Newcastle disease virus (NDV) is a bird killer that has been controlled by routine vaccination in the developed world. Molecular biologist Angela Rmer-Oberdrfer of the Friedrich-Loeffler-Institut in Germany and her colleagues inserted a gene controlling expression of a key flu protein into NDV's genome. The resulting vaccine proved nonlethal in chicks and provoked NDV and flu antibodies in 92 percent of inoculated chickens after three weeks. Vaccinated chickens proved immune to infection by NDV and the H5N2 flu strain that provided the original gene. Naive chickens exposed to either disease invariably died.

Microbiologist Peter Palese of the Mount Sinai School of Medicine and his colleagues achieved similar results with a different strain of bird flu: H7N7. Their vaccine protected 100 percent of the birds against NDV and 90 percent against H7N7. Both vaccines also have the benefit of producing antibodies that are easy to test for, making it simple to ensure that no unvaccinated birds harbor the viruses within a flock.

NDV vaccines can be administered via drinking water, making these combined virus vaccines an effective and potentially inexpensive means of fighting the diseases. And although another strain--H5N1--is creating the most concern for humans, the approach should prove applicable to any variety of flu. "By reverse genetics, a new recombinant NDV carrying [a protein] derived from a currently circulating field strain [of flu] could be generated in roughly four to five weeks," Rmer-Oberdrfer and her colleagues write. "This technique enables the construction of tailor-made matching vaccine in a very short period." Both papers are being published online this week by the Proceedings of the National Academy of Sciences.