The World Health Organization (WHO) said today that between two and 7.4 million people could die in a global influenza pandemic to distance itself from a top UN official's figure of up to 150 million.
Dr David Nabarro, named yesterday as the UN co-ordinator for global readiness against an outbreak, had said that the world response would determine whether a flu virus ends up killing five million or as many as 150 million.
WHO influenza spokesman Dick Thompson
The top figure, which was widely quoted in news reports, would be some three times the toll from the most lethal flu pandemic so far recorded - the 1918-19 "Spanish flu" outbreak in which up to 50 million may have died.
"There is obvious confusion, and I think that has to be straightened out. I don't think you will hear Dr Nabarro say the same sort of thing again," WHO influenza spokesman Dick Thompson told a news briefing.
The WHO, the UN health agency, conceded that all forecasts were guesswork and said Mr Nabarro's comments had merely reflected widely diverging expert opinion.
Mr Thompson said the UN's long-standing forecast of two million to 7.4 million, which comes from a study by the US-based Centers for Disease Control (CDC), was
"the most reasoned position".
But the UN health agency is very worried about the latest strain of avian flu - so-called bird flu - which has hit a number of Asian countries and which it fears has the potential to trigger a new pandemic.
It says the current H5N1 strain of bird flu cannot be easily transmitted among humans, but it is monitoring the virus to see whether there are any genetic changes that could make it become more lethal and spread more rapidly.
"We believe and are very concerned that this virus - which is now widely circulating in the environment and moving west - has the potential to ignite a pandemic," Mr Thompson said.
So far, the H5N1 virus has mainly infected humans who were in close contact with infected birds and has killed 66 people in four Asian nations - Thailand, Vietnam, Indonesia and Cambodia - since late 2003.
The virus has also been found in birds in Russia and Europe. There were three pandemics in the last century. The last two, in 1957 and 1968, each caused between one and four million excess deaths, according to the WHO.
Seasonal flu normally kills up to 500,000 in any year. Only when a pandemic begins will experts really be able to assess its fatality rate.
"You could pick almost any number. There is this vast range of numbers . . . all of this is guesswork, nobody knows," Mr Thompson said.