Oct. 30, 2009 (United Press International) -- Unprecedented demand in Canada's largest-ever mass inoculation program has led to a shortage of the H1N1 flu vaccine, federal officials said.

Various provincial health ministries said the federal health department had notified them "there will be significantly less vaccine delivered than had been anticipated in the weeks ahead," the Canwest News Service reported Friday.

Clinics opened this week across Canada for those at highest risk of contracting what was originally called swine flu, such as children up to five years old, pregnant women and those with lung disorders.

However, thousands of people outside those groups have swamped clinics, and vaccine manufacturer GlaxoSmithKline (NYSE:GSK) was struggling to keep up with demand, the Globe and Mail reported.

When the virus first surfaced in Mexico earlier this year, the Canadian government said it had ordered 50 million doses of the vaccine for the country's 33.7 million citizens.

Federal Health Minister Leona Aglukkaq said Thursday the goal is to have all Canadians who want the shot immunized by Christmas and "we remain on track to meet this goal," Canwest reported.

She said six million vaccine doses will be delivered to provinces by the end of Friday, and another three million next week, the Globe said.