Avian flu - caught directly from birds, and which kills in seven cases out of 10 - could suddenly sweep through the human population, killing 70 million people according to World Health Organisation estimates, a Nobel laureate warned yesterday.
Peter Doherty, of the University of Melbourne, who shared the 1996 Nobel prize for medicine, was speaking at an assembly of laureates in Lyon, France, 50 years to the day after the first announcement of an effective vaccine against the crippling disease poliomyelitis. World health teams hope to eliminate polio altogether by the end of 2005. But, Prof Doherty warned the Biovision conference, there were more immediate hazards.
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Avian flu has killed people who worked with poultry in south-east Asia. Prof Doherty warned that a simultaneous epidemic of human and bird flu could prove a lethal mix, opening the way for the two viruses to mutate into a dangerous infection that could spread swiftly through the human population.
"If it comes, it will probably come out of somewhere like south-east Asia and it will probably come very fast," he said. "It is highly lethal in birds, and in humans, when they catch it, it is something like 70% lethal. So it is very dangerous."
Influenza is a very simple virus with a genetic code in eight segments that can only replicate in an infected host. If a human infected with flu from ducks was also infected with human flu, then the two viruses could reassort themselves: swap genes. It happened 30 years ago, with Hong Kong flu, which also began in ducks, he said. In countries like Cambodia and Vietnam, where influenza vaccines were rare, a human version of avian flu would spread rapidly.
Governments had begun to stockpile an antiviral called Tamiflu, which was effective if taken early enough. "But if we got a real outbreak ... with massive numbers of cases there would probably be enough Tamiflu to protect key medical professionals, perhaps politicians ... it is whether there is enough of it around," he said.
Scientists in Britain, China and the US were racing to devise new vaccines. Researchers at the National Institute for Biological Standards in London are using a new technique called reverse genetics, to detach proteins from the surface of a standard strand of flu vaccine, and replace it with proteins from avian flu. This would mean that vaccines could be "grown" very swiftly.
"The interesting thing is that it would be, as a vaccine, a genuinely genetically modified organism, a GMO. Will the Europeans take a GMO when it is injected in their arms and saving their lives from flu? We shall see," Prof Doherty said.
Three years ago, severe acute respiratory syndrome - Sars - had been dangerous but slow to infect, he said. But influenza moved swiftly. In the world's most catastrophic pandemic, the Spanish influenza outbreak of 1918, the global death toll was estimated at more than 40 million. People travelled slowly then - by sea - but the virus still reached almost the entire world. Now people moved from one continent to another in a day, the global population had trebled, and people were more likely to defy attempts to impose quarantine.
"We may duck the bullet. We may be lucky. But I think it is a reasonably high probability, because you have a lot of human flu," Prof Doherty said. "We will always have flu epidemics. Once the thing hits, we would deal with it extraordinarily well."
