Canada will purchase more than 50 million pandemic flu vaccination doses for the upcoming season, Health Minister Leona Aglukkaq said Thursday.

She added that Ottawa will cover 60 per cent of the costs and will ensure that it is available for any Canadian who wants it.

However, it isn't yet known if some patients will need two doses in order to combat the illness. Officials should have a better idea of how the vaccine works in the coming weeks, as clinical trials begin.

The order will cost more than $400 million, according to Dr. David Butler-Jones, head of the Public Health Agency of Canada.

GlaxoSmithKline has won the contract to manufacture the vaccines. It's expected GSK will start clinical trials by October at the latest.

If all goes well and the trials indicate the product is safe and effective, immunization programs will most likely begin in November.

The vaccines will be produced at the company's facility in Ste-Foy, Que., which is nearby the provincial capital of Quebec City.

The announcement comes as the World Health Organization said the development of a swine flu vaccine is "on track," and the first vaccines should be ready for use in some countries by September.

Dr. Marie-Paule Kieny, director of the WHO's Initiative for Vaccine Research, says manufacturers have completed small batches of the pandemic vaccine and are now starting clinical trials to test both it s effectiveness and its safety.

She says clinical trials have already started in Australia, China, the United States and Germany.

Kieny notes that before vaccination programs can begin, regulatory agencies in various countries must first license the vaccines.

Dr. Kieny said manufacturers had initially reported poor yields in making vaccine, leading to worries about supplies. This is now improving, she told reporters Thursday morning.

"We are on track in development," Kieny said. But she declined to offer an updated prediction of how much vaccine will be available.

"I would really like to avoid making any projection right now," she said, noting she would like to see data on yields from new strains of the virus being provided to vaccine manufacturers before revising production estimates.

The first batch of seed strains available to manufacturers produced disappointingly low virus yields. Manufacturers reported getting somewhere between one-quarter and one-half of the yield with the pandemic virus seed strains that they normally get with seasonal flu vaccine production.

A new and better seed strain has been developed and was shipped this week to manufacturers, including GSK in Canada.

The lab that made the new strain, Britain's National Institute for Biological Standards and Control, says the new strain produces a yield that is comparable to that of seasonal flu vaccine.