HONG KONG, July 13: Three vaccines used to prevent respiratory disease in chickens have swapped genes, producing two lethal new strains that have killed tens of thousands of fowl across two states in Australia, scientists reported today. The creation of the deadly new variant was only possible because the vaccines contained live viruses, even though they were weakened forms, said Joanne Devlin, lead author of the paper published in the journal Science. (agencies)
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