TORONTO - Ontario residents in high-risk groups can start rolling up their sleeves Monday to get the swine flu vaccine -- about a week ahead of schedule -- now that Ottawa has given its stamp of approval, provincial health officials said Wednesday.

"It is our most effective weapon in fighting H1N1," said Health Minister Deb Matthews, who added she plans to get the vaccine.

"We are ready, we are prepared, and we are going to win this battle one shot at a time."

About 722,000 doses of the vaccine that arrived Saturday are already en route to the province's 36 local health units and will be offered to certain high-risk groups first, said Dr. Arlene King, Ontario's chief medical officer of health.

They include adults under the age of 65 with chronic conditions, health-care workers, caregivers for high-risk groups, people living in remote and isolated communities, pregnant women and healthy children six months to five years of age.

Everyone else may have to wait until mid-November or December to get the vaccine, depending on how quickly Ottawa replenishes Ontario's stocks, King said. All who want the vaccine should be immunized by Christmas.

Some pregnant women, who were supposed to be at the front of the line for the vaccine, may also have to wait.

The H1N1 shot intended for pregnant women is not expected to be available for at least two more weeks, King said.

Expectant mothers more than 20 weeks into their pregnancy, or who have underlying medical conditions such as asthma and diabetes, should therefore talk to their doctors about getting the vaccine that's already arrived, she said.

Healthy women in the first half of their pregnancy should wait for the flu shot that doesn't contain an adjuvant -- a natural additive that boosts the impact of a vaccine -- because there's less risk they'll develop complications from the flu, King said.

The unadjuvanted vaccine won't be available until early November, and even then, it takes 10 to 14 days to take effect, she said.

"I don't know how much more flu activity we will have at that time, but it could be significant," she said. "And I think on balance this is the best recommendation I can make."

Her advice coincides with what federal health officials were saying last Friday when they advised pregnant women to get the adjuvanted vaccine that will be offered to everyone if they're concerned that they could become infected with the H1N1 virus.

At the time, King stuck to her recommendation that all expectant mothers wait and take the unadjuvanted vaccine, given the concerns about its safety.

But she changed her mind Monday, given that H1N1 cases are "going up fairly rapidly" in Ontario and it's still uncertain when the unadjuvanted vaccine will arrive.

"So really, it's a matter of weighing risks and benefits, and we have to be responsive," King said.

"As I said, this is real-time science influencing real-time policy, informing real-time communication."

Until now there had been no licensed flu vaccine containing adjuvant in Canada, although adjuvants have been used for years in Europe in flu vaccines targeted at seniors.

There is no data on the use of adjuvanted flu vaccine in pregnant women and little data on the safety of the additives in vaccines given to children.

Ontario residents will have to contact their local health unit to find out where to get the H1N1 vaccine, which may not be available through their family doctors.

That's because the adjuvant must be added to the vaccine and administered to 10 people within 24 hours, according to health officials.

Anyone over the age of 10 will only need one dose for full immunity against the swine flu instead of two, as previously thought, King said. Children under 10 will require two half-doses, given at a minimum of 21 days apart.

People over 65 seem to have an immunity to the H1N1 virus and are being asked to get the seasonal flu shot only for now, although they'll be able to get the swine flu vaccine later if they want it.

King said there have been 27 deaths from H1N1 in Ontario and infection rates are climbing, but stopped short of confirming that the second wave has arrived in the province.

"We have had more hospitalizations over the course of the last week," she said. "We currently have 26 hospitalizations, and that's more than we had a week or so ago."

On Tuesday, King reported that a turkey breeding operation in southern Ontario was hit by the H1N1 virus, but that it likely poses no risk to human health because the birds were not destined for the food chain.

It was only the second time turkeys have been reported to have been infected with the pandemic virus -- the first was in Chile in August.