According to the news, whether the bird flu will cause a great casualty depends

Within the last few minutes the UN official responsible for bird flu has told us he stands by his assessment that a pandemic could kill as many as 150 million people. But Dr. David Nabarro admitted that much depends on the type and the location of a flu outbreak. He says the UN is putting a strategy in place to deal with the threat of a pandemic.
     The UN’s new coordinator for avian and human influenza said he was almost certain there could be another major outbreak of influenza soon. He said the likelihood that the virus which has caused bird flu in Asia could mutate and jump to humans was high. Dr. Nabarro stressed he will be working hard to control bird flu through contact with farming communities and markets where birds are sold, and looking at the migration of wild birds. Dr. Nabarro said the number of deaths from any future influenza pandemic would depend on where it started, how quickly it was discovered, and the kind of response they got from governments.