Jean-Marc Olive, the WHO representative in Manila, said, "The next pandemic may cause very high morbidity and mortality in a few weeks. It could cause one billion cases and two to seven million deaths."
Olive made the statement during a forum held at the Australian embassy in Makati City Tuesday. WHO based the grim scenario on previous flu epidemics.
The WHO official added that even "a modest pandemic lasting over one year might cause losses as high as three percent of Asia's gross domestic product and 0.5 percent of world GDP."
Since 2003, a total of 172 people have died from the deadly H5N1 strain of bird flu, mostly in Southeast Asia. However, the majority of infections came from direct contact with birds infected with the virus.
Scientists fear the virus could mutate and allow human-to-human transfer.
The organization said the evolution of the threat posed by bird flu "cannot be predicted."
The WHO official suggested that mass culling of poultry must be undertaken to prevent a human pandemic and that governments should boost their capability to prevent the spread of the disease, strengthen surveillance and prepare for any outbreak.
A recent exercise simulating an outbreak of bird flu in Cambodia showed that the world body could deliver a large supply of Tamiflu, a medicine used to treat human cases, to an affected country in two days.
