VANCOUVER -- If the avian flu outbreaks in Asia give rise to a new virus that proves virulent to humans, Canadian health officials will likely turn to chickens to produce a vaccine.

Perry Kendall, provincial health officer for British Columbia, said a national strategy that is still under development in Canada has identified "a national flock of chickens" that could be used if a pandemic were to break out.

The chickens would be used to produce eggs in which the seed virus for a new vaccine would be cultured.

The death of a woman in Thailand last week, in an apparent human-to-human transference of avian flu, has heightened concerns that a new, mutated virus could emerge, unleashing a global pandemic.

Although the World Health Organization thinks it is a "dead-end incident" that won´t go beyond one isolated case, it has served as a reminder that avian flu poses a potentially serious threat to human health.

Dr. Kendall said the fear is that an avian flu virus could mutate or mix with human influenza virus, creating a form that spreads as easily among humans as it does among chickens.

In that event, a pandemic would be unleashed. Experts have speculated that such a pandemic could kill 280,000 to 650,000 people in the industrialized world before it is contained.

Dr. Kendall said it´s not possible to build a massive stockpile of vaccines, or to inoculate an entire population in advance, because nobody can predict exactly what the new, or mutated virus will be like.

That means health officials have to come up with a strategy for making new vaccines as quickly as possible once the new virus has been identified.

That´s where the national flock of chickens comes in.

"To make a vaccine you have to have the virus that is going to be causing the pandemic. Or you have to make a guess about the virus. . . . You then have to start making what are called seed-strain viruses," Dr. Kendall said.

Flu viruses are grown in egg cultures, which means that thousands of eggs would be needed overnight by health officials.

"Fortunately, we have got a capacity in Canada of having a constant, very large flock of chickens who are constantly producing eggs, so that as soon as you identify a seed-strain virus, you can go into limited production of a vaccine," Dr. Kendall said.

"It´s a special flock of chickens that are raised to maturity and bred to provide a constant supply of eggs, otherwise you´d have to wait five months to get enough chickens to lay eggs to produce the vaccine. This shortens the process because we always have, at all times, a sufficient number of chickens to produce several million doses of vaccines."

But even that isn´t going to provide enough vaccine fast enough.

Dr. Kendall said it takes months to produce a vaccine from scratch.

By then the virus could have spread around the world.

"It´s anticipated that within anything from two to six months of a pandemic strain being identified and getting loose, it´ll be globally spread . . . [so] you´re not going to have a vaccine for that first wave. But you are going to have limited amounts of vaccine after that. You won´t have 30 million doses, but you might have 8 or 10 million doses."

Dr. Kendall said that with such a shortfall, health officials would have to have a priority list. Health-care workers and other front-line responders, as well as those in the population judged most at risk, would be among the first inoculated.

He said groups of health experts have been working on priority lists, so that in an emergency a limited amount of vaccine can be used in the most effective way.

"You´d look at providing health care and maintaining a civil society and trying to stop the very vulnerable from becoming ill," Dr. Kendall said.