The "very frightening" outbreak of virulent bird flu in Asia could lead to the most devastating human pandemic in history - or it could continue just to produce isolated deaths of people who are in close contact with poultry, the chief influenza scientist at the US Centres for Disease Control said yesterday.

Dr Nancy Cox told the American Association for the Advancement of Science: "There is a real challenge in public health in mobilising people into action without trying to scare them to death. If we knew for sure that a pandemic with, say, a 10 per cent fatality rate was going to occur, we could proceed in a more deliberate way."