The H1N1 influenza vaccine is now available across most of Canada to health-care workers and people considered at a higher risk for complications from the respiratory illness.

Eligible groups include individuals under the age of 65 who have chronic medical conditions, as well as pregnant women, children under the age of five and people living in First Nations or remote and isolated communities.

Ottawa approved the vaccine last Wednesday.

Clinical trials worldwide suggest that up to 85 per cent of healthy adults who are vaccinated will develop immunity within 10 days.

The availability of the vaccine differs from region to region, but in most cases people can get the shot this week — some as early as Monday. New Brunswick and Quebec have already started their mass immunization programs. In Ontario, health-care workers are first up for the H1N1 vaccine.

Dr. Arlene King, Ontario's chief medical officer of health, said there will be enough vaccine for everyone who needs it.

Although medical officials in some provinces have said that no one will be turned away if they arrive to get the vaccine, health officials such as those in Alberta are encouraging that Canadians who are not in a high-risk group wait their turn. Vaccinations are expected to continue throughout November and December and are free.

2nd wave of pandemic

On Monday, U.S. Health and Human Services Secretary Kathleen Sebelius acknowledged frustrating waits for the H1N1 vaccine in the U.S., where about 16.5 million doses have been made available.

Sebelius told ABC's Good Morning America she doesn't think the H1N1 vaccination campaign is too late.

"What we saw in [the 1957-58 flu pandemic] was that there was a big outbreak in fall and then a new wave in the spring."

On Saturday, U.S. President Barack Obama declared the swine flu outbreak a national emergency. The White House said that declaration will make it easier for health-care workers to handle a surge in swine flu patients.

Also on Saturday, Dr. David Butler-Jones, Canada's chief public health officer, said Canada's system differs from that of the U.S., and that antiviral medications and the H1N1 vaccine have already been sent out to provinces and territories to distribute.

Canada has entered the second wave of the pandemic phase, which means there has been an increase in the number of swine flu cases across the country.

Canadians can talk to their family doctor or public health nurse to get the facts about the vaccine, Health Minister Leona Aglukkaq suggested last week.

Swine flu remains a disease in which the bulk of illnesses and hospitalizations occur among young people, a common characteristic of pandemic flu viruses.

In Canada, the median age of those who have become ill with laboratory-confirmed swine flu is 21, and the median age of those who died is 51.

With files from The Canadian Press