The warning comes from researchers who used computer models to investigate what would happen if the bird flu virus, which is currently rife among poultry in areas of Cambodia, Thailand and Viet Nam, mutated into a form that could spread easily among humans.

Global Epidemic Inevitable?

Scientists believe it is only a matter of time before the virus, known as H5N1, mutates to become more infectious to humans, possibly by swapping genes with the human flu virus.

"This is the event we are all scared might happen at any time," said Neil Ferguson of Imperial College London and the leading author of the study. "We'd be faced with an event worse than the 1918 Spanish flu pandemic."

The avian flu virus has killed more than 50 people in Asia, more than half of those who have been infected. Almost every death was traced back to the person coming into contact with infected poultry in the countryside. The Spanish pandemic of 1918 is believed to have claimed up to 40 million lives worldwide.

Professor Ferguson's team modeled the spread of a mutated bird flu virus among 85 million people living in Thailand and a strip of neighboring countries.

Early Detection Essential

After watching how quickly the virus spread around the globe, they tested various strategies for containing an outbreak. "Until now, the idea of stopping an outbreak hadn't been investigated," he said.

If an outbreak was detected in its infancy, with less than 50 people infected, models show it could be contained by administering antiviral drugs to the 20,000 people closest to those infected, the researchers reported in the journal Nature yesterday.

Combined with other measures, such as shutting schools and workplaces, it would take around 60 days to contain the outbreak, with the number of cases totaling no more than around 200.

To deal with the worst-case scenario of a bird flu outbreak, the scientists called for an international stockpile of 3 million courses of antiviral drugs to be set up, ready to be deployed anywhere in the world within a few days of an outbreak being detected.

Global Race to Stockpile Antiviral Drugs

A spokeswoman for Roche, which manufactures the antiviral drug Tamiflu, confirmed that the company is in talks with the World Health Organization (WHO) about building a stockpile of the drug, but refused to give further details.

The WHO already has 120,000 courses of Tamiflu, but with Britain and France each waiting for orders of 15 million courses from Roche, the company will have to decide which takes priority.

Professor Ferguson's research was reported alongside a second study published online yesterday by the US journal Science, which modeled an outbreak of flu among half a million people living in Thailand.