Amanda O'Jaick is expecting twins and held off getting vaccinated until Thursday, when the non-adjuvanted H1N1 vaccine became available in Ottawa. (CBC)

Health Canada has approved the use of adjuvant-free swine flu vaccine made in Canada for pregnant women and healthy people aged 10 to 64, federal health officials announced Friday.

The new vaccine has already been sent to provinces and territories, which may start using it immediately, said Dr. Elwyn Griffiths, director general of the biologics and genetic therapies directorate at Health Canada, which authorizes use of vaccines.

In British Columbia, which had the adjuvant-free vaccine shipped ahead of approval, people should be able to get the vaccine doses starting late this weekend or early next week, said Dr. Perry Kendall, the province's health officer. The vaccine should be available at the same time in other provinces, he said.

Up to 1.8 million doses of the adjuvant-free vaccine from GlaxoSmithKline will eventually be available to Canadians, said Dr. David Butler-Jones, Canada's chief public health officer.

"Using the unadjuvanted vaccine will allow more Canadians to be immunized sooner," Butler-Jones said at a news conference. "This vaccine has been shown to be very effective in those with healthy immune systems."

So far, about 25 per cent of Canadians have received H1N1 shots, Butler-Jones said. By next week, there should be enough of both adjuvant-containing and adjuvant-free vaccine to immunize one-third of Canadians.

Adjuvants are additives that boost the immune system's response to a vaccine. The H1N1 vaccine targets the strain of H1N1 influenza A virus causing the current swine flu pandemic.

Adjuvant-free vaccine no longer recommended for young children

Ottawa initially ordered the adjuvant-free vaccine for use by pregnant women and young children, since there is a lack of clinical data around the use of adjuvants in these two groups.

But when data started showing that the adjuvant version offers better immune protection for children under three years of age, federal health officials decided to offer some of the adjuvant-free doses to Canadians aged 10 to 64 with a healthy immune system.

In young children, the immune system is still developing, and they don't respond as well to vaccines without adjuvants.

For babies and toddlers, the adjuvant vaccine is "clearly superior and very safe," Butler-Jones said.

The adjuvant-free vaccine provides 94 per cent immunity, compared with 60 to 80 per cent immunity conferred by seasonal flu shots, federal health officials said.

The federal government also purchased and distributed 200,000 doses of adjuvant-free vaccine from Australian manufacturer CSL, which Canadian pregnant women started receiving this week.

A total of 8.5 million doses of adjuvant vaccine have also been distributed to provinces and territories.

About 300,000 to 350,000 women get pregnant each year in Canada, and 200,000 to 250,000 are pregnant at any given time, Butler-Jones said.