The H1N1 vaccine has been approved for rollout across Canada, Health Minister Leona Aglukkaq announced Wednesday.

"I'm happy to say that today Health Canada has authorized the H1N1 flu virus vaccine," Aglukkaq told an Ottawa news conference. "This is a milestone in our efforts to fight H1N1 flu virus."

She encouraged all Canadians to get the vaccine once it is available in their community, as early as next week.

Health Minister Leona Aglukkaq laughs as she shakes hands with chief public health officer Dr. David Butler-Jones following a news conference in Ottawa to announce that Canada has approved an H1N1 flu vaccine. (Adrian Wyld/Canadian Press)

The overriding objective in reviewing the H1N1 influenza A vaccine, called Arepanrix, was to protect the health and safety of Canadians, she said. Health Canada will continue to monitor use of the vaccine in collaboration with regulators worldwide.

The announcement means the vaccine performed as expected in tests, and most people will gain immunity within 10 days of receiving one dose, said Dr. David Butler-Jones, Canada's chief public health officer.

Typically, seasonal flu shots offer 60 to 80 per cent immunity. So far, one dose of the H1N1 vaccine seems to offer immunity in the "high 90s" in healthy adults, Butler-Jones said.

The federal government shipped more than two million doses of the pandemic vaccine across the country in anticipation of the approval.

Priority for health-care workers

Canadian clinical trials started this week. Federal health officials approved the vaccine for use by the general public based on clinical trial data in Europe.

Other countries, including the United States, Japan, Britain, Australia and China, have already started giving the vaccine to certain segments of their populations, such as health-care workers.

The first doses of the H1N1 vaccine are meant for those at high risk. (Jack Dempsey/Associated Press)

Canadian public health officials are urging those most vulnerable to serious complications from the virus — such as pregnant women, young children, people living in remote and isolated communities, and adults with chronic conditions like asthma — to consider getting the vaccine as soon as it becomes available where they live.

Provinces, territories and local health regions will decide who will get the vaccine first. British Columbia's health officer, Dr. Perry Kendall, urged patience.

"We'll be asking other people to hold back," Kendall told reporters. "I think we can trust British Columbians and Canadians to understand the importance of reaching the most vulnerable."

Wednesday's approval only applies to a form of the vaccine that contains an adjuvant, a booster designed to make the vaccine more effective.

The federal government has also ordered 1.8 million doses without the adjuvant for use by pregnant women and young children, since there is little data on the safety of the additive in those groups.

Vaccine dosing

Health Canada is expected to approve the vaccine without the adjuvant in a week or two.

Butler-Jones also outlined recommendations for giving the vaccine, namely:

• Children over six months of age and under 10: two half doses at least 21 days apart.
• Age 10 or older: one full dose of adjuvanted vaccine.
• Pregnant women: one full dose of unadjuvanted vaccine. If that is not available and H1N1 rates are high or increasing, women more than 20 weeks into their pregnancy may be offered the version with the adjuvant.
• Under six months of age: not authorized.

The reason for the 20-week guideline for pregnant women is that most of the risk seems to occur in the latter part of pregnancy, Butler-Jones explained. But pregnant women with an underlying health condition such as diabetes should talk to their health-care provider about getting the adjuvanted form of the vaccine.

Initially, Canadian experts considered offering the unadjuvanted form for children under age three. But limited data on the unadjuvanted form suggests it is not as effective for that age group, and the adjuvant is now the recommended version for young children, said Dr. Carolyn Pim, senior medical adviser at the Public Health Agency of Canada.

Some doses of unadjuvanted form will also be reserved for those who wish to use it in young children, Pim added.

Both versions of the vaccine in Canada used a killed virus that cannot cause infection, Butler-Jones said. The adjuvant is made with fish oil, water and Vitamin E, and has been used in tetanus, hepatitis and diphtheria vaccines, he added.

Young people hit hard in U.S.

So far in Canada, there have been 83 deaths, more than 1,500 hospitalizations and close to 300 admissions to intensive care from the H1N1 virus in Canada, Butler-Jones noted.

The H1N1 virus seems particularly dangerous for young people. Half the U.S. deaths involved teenagers and one-third occurred in people without underlying conditions, which shows the virus should be taken seriously, Butler-Jones said.

This will be the largest mass immunization campaign in Canadian history, Kendall said.

New Brunswick will start vaccinations on Thursday. Other Atlantic provinces are also rolling out vaccine clinics quickly, and the rest of the country will start immunizing people early next week.

British Columbia and the Northwest Territories are experiencing outbreaks of H1N1, and there have been sporadic cases across the country since the virus first emerged in the spring.

The federal government has a contract with GlaxoSmithKline, which will produce 50.4 million doses of the pandemic vaccine at its facility in Quebec City. The company also makes the seasonal flu vaccine.

Aglukkaq said no decision has been made on whether Canada will share extra vaccine supplies with other countries, as the World Health Organization has requested.

Health Canada will continue to monitor use of the vaccine in collaboration with regulators worldwide.

With files from The Canadian Press