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Dr. Richard Schabas, Ontario's former chief medical officer.

Scientists are divided about whether sporadic cases of the deadly H5N1 strain of avian flu in humans means a global pandemic is nearing.

The human health impact of H5N1 has been minimal, compared to killers like malaria and AIDS.

"If you're a bird, it's a pandemic," said Mike Leavitt, the U.S. human health secretary in Washington. "If you're a human being, it's not."

H5N1 is one of the most lethal viruses to infect birds, but it has not gained the genetic changes needed to transmit easily from person to person.

"Those pundits who have been predicting disaster all this time," said Dr. Richard Schabas, Ontario's former chief medical officer. "I think it's time for them to take a good hard look at what has happened and what hasn't happened, and maybe re-evaluate their assessment."

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Dr. Todd Hatchette says it's difficult to predict which viruses may trigger a pandemic.

As days pass without H5N1 altering its behaviour in humans, the chances of it triggering a pandemic are reduced, Schabas said.

Not necessarily, says Dr. Todd Hatchette, a virologist at Dalhousie University in Halifax.

"We don't know exactly what influenza needs to become effectively transmitted human to human," said Hatchette. "We don't know when it's going to happen. And because we don't know what it needs, we can't predict which virus is going to be the one that becomes the next pandemic."

World Health Organization officials are urging countries to prepare for a pandemic that could kill millions of people. They point to H5N1 as the strain most likely to trigger one.

Sometimes the nuances of the message get lost, said Dick Thompson, a spokesperson for the UN body in Geneva.

"We have to get across the complete message: this is a dangerous virus, but we don't know when or if it's going to transform into a pandemic virus."

Schabas agrees that another flu pandemic will hit in the next few decades. But he doesn't think it will be as devastating as the Spanish flu pandemic of 1918, saying some preparedness is appropriate but the current panic is not.

By stockpiling drugs with a limited shelf life and making vaccines for H5N1, governments are wasting scarce resources and fuelling public panic, Schabas said.

On the other hand, his critics don't see evidence of panic; they feel it's just proper emergency planning.