A year ago, H5N1 avian flu was ripping through Asian poultry flocks and sparking frequent - and too often fatal - human infections in Vietnam. International health authorities worried that a largely oblivious world might be sleepwalking toward disaster.

Few are ignoring the persistent and virulent virus now. But with awareness mounting and fear surging, some of the people who earlier sounded the alarm are wondering if it's time to adjust the volume - or at least fine-tune the channel.

Some express concern that nuances of the actual risk are being lost as the virus continues its flight across Asia, Africa, the Middle East and Europe.

Dick Thompson, the World Health Organization's spokesperson on the issue, worries people have come to - or have been led to - the conclusion that a pandemic arising from this strain of avian influenza is inevitable.

"When we initially started talking about this and to today, we were always saying: We don't know if H5 is going to be the virus, we don't know if it is going to be a bad pandemic, when it will strike, any of that stuff," Thompson says from Geneva.

"All of that seems to me now lost. It seems to me that in everything I'm reading, it's a lock."

Flu virologist Adolfo Garcia-Sastre, who remains skeptical that H5N1 will become a pandemic virus, voices similar concerns. He worries people will become complacent about influenza if this threat subsides.

"This is something I'm a little bit afraid of," Garcia-Sastre says from New York, where he works at Mount Sinai School of Medicine.

"If H5 doesn't make it into a pandemic - and I don't want H5 to make it into a pandemic - but if the virus doesn't make it that somehow people will feel betrayed by all the publicity that was given to the virus."

Thompson's fear is that people will lose faith in public health authorities if the public overlooks the caveats attached to the warning messages.

"We earned a lot of trust during SARS and we could blow it all on H5N1," he says of the WHO.

"But I don't think that that's a big gamble as long as people understand exactly what we're saying. And it's not a bumper-sticker statement. It's a complicated statement. And that is: 'We don't know what the next pandemic is going to look like or how bad it's going to be. But there will be a pandemic and if you prepare for it you can reduce the damage.' "

In many respects, the timing of such qualms seems odd. In recent months, the virus has vastly expanded its geographic range, sparking human infections far beyond its original epicentre of Southeast Asia.

After warning for so long that H5N1 is a significant threat, why get cold feet about that message when the virus seems to be proving your point?

Dr. Jody Lanard, a risk communications expert, isn't surprised by the seeming contradiction.

"There is a kind of seesaw of attention between the public and officials," says Lanard.

"When everyone is ignoring the problem, officials focus on raising the alarm. When people finally pay attention and start worrying, the officials instantly want to calm them down again.

"Everybody in the warning business worries that people will accuse them of crying wolf," she adds. "They forget that in the actual Boy Who Cried Wolf story, the wolf finally showed up."

Dr. Michael Osterholm, a favourite target for those who see the warnings about H5N1 are unwarranted, has some sympathy for Thompson's fears. Up to a point.

"I think it's a very legitimate concern," says Osterholm, who has been one of the most vocal proponents for pandemic preparedness.

"And unfortunately for those of us who have been trying to bring the world to a much higher state of preparedness for pandemic influenza, we have to live often by an eight-word or nine-second sound bite out of a much larger comprehensive message."

Osterholm readily acknowledges there is no way of knowing what strain will cause the next pandemic or whether H5N1 will become a pandemic strain.

But he frequently warns of the parallels between H5N1 and the influenza strain that triggered the 1918 Spanish Flu - earning the disdain of those who insist the severity of that pandemic could not be replicated in the era of modern medicine.

"I worry that too many policy leaders dance around this issue fearful that somehow they will either offend or frighten the public," says Osterholm, the director of the Center for Infectious Disease Policy and Research at the University of Minnesota.

"Our job is not to upset people or to calm people. Our job is to tell the truth."

The job is also to accelerate preparations for a flu pandemic that will come one day, regardless of the H and N numbers on the eventual pandemic strain's name, says Dr. Keiji Fukuda, head of the WHO's global influenza program.

"We are not magicians. We cannot predict what's going to happen tomorrow. But we can say that there are things that we should be concerned about and there are things that we can do because of those concerns."

Fukuda is not worried about expectations.

"If confidence is built on our ability to predict the short-term future, it is confidence which is misplaced. On the other hand, if it is confidence that these are institutions that are analyzing the situation, looking over it and making recommendations, making moves which really are important moves and good moves, that is why trust should be placed in public health."