Figures raised in public discussion of the pandemic threat range from a low of two million to this figure of 100 million, advanced Monday by Dr. Shigeru Omi, WHO director for the Western Pacific region. Privately flu experts debate the possibility the numbers could be significantly higher still.

While the WHO - the source of some of the inconsistency - plans to come up with a better range of numbers, many experts warn against becoming too fixated on figures.

They want people to keep their eyes on the forest, not stop to count trees.

"We need the world leadership to understand what´s before us," leading U.S. epidemiologist Michael Osterholm said Monday.

"These are not statements made to scare people out of their wits. They´re statements made to scare people into their wits."

There is growing concern that the aggressive strain of avian influenza that has been ravaging poultry stocks in Asia for much of the past year will acquire the ability to easily transmit to and among humans, who have no immunity to it.

The prospect of a pandemic fuelled by the H5N1 strain strikes fear in hearts of infectious disease experts and public health officials because of the strain´s incredible virulence to date.

As they urge governments to speed up pandemic planning, experts have been projecting fatality rates which are in reality best guesstimates based on what is known about the attack rates and fatality rates of pandemics of the 20th century.

The experts need numbers to garner attention and quantify the risk for policymakers faced with the daily challenge to decide where scarce public funds are spent.

But big numbers are a double-edged sword, admitted Dr. Keiji Fukuda, a leading flu expert at the U.S. Centers for Disease Control. They can both open eyes and, if they are large enough, instil a sense of helplessness - something experts hope to avoid.

"They certainly can get initial attention. But the important thing is getting initial attention and then having sustained attention so that the steps that need to be taken are taken," Fukuda said.

In reality, at this point no one can know how many people a pandemic would kill.

"If your question is ´How many people are going to die from the next pandemic?´ the only reasonable answer is: ´We don´t know,´ " said Dick Thompson, communications director of the WHO´s communicable diseases branch.

But Thompson, who has fielded questions about why different WHO officials are using different projections, said the agency has to get a better handle on the risk.

"We need to be able to calibrate our level of concern," he said. "We need to set boundaries on the conservative and least conservative estimates of deaths from the next pandemic."

Fixating on death estimates won´t accurately prepare the public for what is to come, said Martin Meltzer, the health economist who produced the most commonly cited projection - two million to seven million deaths.

"The point isn´t the exact number," said Meltzer, who works in the office of surveillance in the CDC´s National Center for Infectious Diseases. (Meltzer calls his oft-quoted range - based on the mild Hong Kong flu of 1968 - "conservatively low.")

"The point is: imagine a lot of people ill in a very short space of time. More than you´ve ever seen.

"And whether it´s seven million or 70 million who die, that´s not going to be the entire experience of the next pandemic flu. There´ll be sick people. There´ll be people requiring medical care. There´ll be people requiring hospital beds."

Osterholm said the wide fluctuation of numbers reflects the fact the scientific world is coming to grips with the realization that a flu pandemic no longer seems merely hypothetical.

"Now we´re at the point of saying: We really have to understand this, because this is for real," said Osterholm, who is director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

"What I think we need to do is move on now and not get caught up into: Is it seven versus 100 million? It probably is somewhere in between.

"But the point of it is, I think we now have to focus on what does this mean for the world? For its economy? For its health? For its political stability? And how are we going to respond?"