Canada will purchase 50.4 million doses of pandemic flu vaccine, an amount that should be sufficient to protect all Canadians who want to be vaccinated against the swine flu virus, federal officials said Thursday.

The order was announced by Health Minister Leona Aglukkaq, who said the federal government would pick up 60 per cent of the $403.2 million tab for the vaccine.

"This investment reflects the unique circumstances of the situation as well as the gravity," said Aglukkaq, who called it a special one-time contribution. She noted that with seasonal flu vaccine purchases, provinces and territories are responsible for 100 per cent of the cost of their programs.

The vaccine will be bought from GlaxoSmithKline, which will make the product at its facility in Ste-Foy, Que.

Dr. David Butler-Jones, head of the Public Health Agency of Canada, said the size of the order should be sufficient to cover all Canadians who want and-or need pandemic vaccine.

"I think there's a fair degree of confidence that the amount that we've ordered will be sufficient," he said in an interview with The Canadian Press.

"Again, I'm waiting to see what the clinical trials show before being definitive."

That is a reference to the fact that it is not currently known whether one or two doses of vaccine will be needed to protect against the new H1N1 virus.

It is thought, though, that older adults - who seem less vulnerable to the virus - may be able to get by with only one dose. And Butler-Jones said because Canada is likely going to be using vaccine containing an adjuvant - a compound that boosts its potency - there is reason to believe one dose may suffice across all age groups.

He explained the federal math this way:

There are 33.6 million Canadians. The federal pandemic plan suggests authorities should bank on 75 per cent of Canadians wanting or needing vaccination. With 50.4 million doses, 75 per cent of Canadians could each get two doses.

But if only one dose is needed for some or all Canadians, different formulas could come into play.

The order size obviously allows for one dose for 100 per cent of Canadians, or one dose for all and a second dose for 50 per cent of the population, if studies show some people need ...[next page]