he swine flu virus which has spread around the world threatening a global pandemic could turn out to be a mild strain, experts now believe.
Official projections have predicted that Britain alone could see 750,000 deaths in the event of a major pandemic, with millions more around the world.
But initial analysis of the particular H1N1 virus concerned suggests that it would have to mutate further to cause the kind of mass fatalities being predicted in some quarters.
In Mexico, the epicentre of the outbreak, the virus is thought to have led to more than 160 deaths but so far it has only been confirmed as the cause in 15 cases in addition to one in the United States.
Mexico's health minister, Jose Angel Cordova, said that it was becoming clear that the new strain was less dangerous than the H5N1 form of bird flu which caused concern around the world in recent years – although more contagious.
"Fortunately the virus is not so aggressive – it's not a case of avian flu, which had a mortality rate of nearly 70 per cent," he said.
Initial analysis of the make-up of the virus backs up his view although experts stress that it cannot be predicted how it will mutate.
The evidence so far suggests that swine flu lodges itself in the upper respiratory tract, around the throat and nose causing coughing and sneezing which in turn help spread it.
But other varieties, such as H5N1, tend to bind further down the respiratory tract, inside the lungs themselves, causing more severe illness.
Professor Wendy Barclay, who holds the chair in influenza virology at Imperial College London, told the BBC: "There are two aspects – one is which receptors the virus tends to bind to and what we see is that it is binding to the upper respiratory tract rather than deep in the lungs."
Scientists at the World Influenza Centre in Mill Hill, London, are beginning to analyse samples of the virus collected in the United States.
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