GOOD NEWS! New Flu Bugs: Too Lethal For a Pandemic? “Calculations by Dr. Boni and his colleagues show that with 60% mortality, H5N1 bird flu is still four times too lethal to be able to spread within a human population. In captive ferrets (the experimental animal of choice for flu research) it is rapidly evolving toward lower virulence. Ironically, the most worrying sign for a bird-flu pandemic would be if the virulence dropped significantly—then it could spread. There are signs this might be happening in Egypt.”