Gordon Potter receives a shot from nurse Wendy Nesheim during the first of several clinical trials of a new H1N1 flu vaccine conducted by Emory University, in Atlanta. (John Amis/AP Photo)

The U.S. Food and Drug Administration has approved new swine flu vaccines, which clears the way for Americans to start getting the shots as early as the beginning of October.

Pregnant women and children will be among those at the front of the line when the first rationed supplies of the pandemic vaccine are distributed early next month, U.S. Health and Human Services Secretary Kathleen Sebelius told Congress on Tuesday.

Vaccines made by Sanofi-Aventis SA, CSL Ltd, Medimmune and Novartis AG were approved, she added. The bulk of the vaccines will be available in the U.S. by mid-October.

Health Canada said it's balancing the need for speed with its duty to make sure a vaccine is safe and effective. It's waiting for the results of Canadian trials which have just started recruiting volunteer test subjects.

Canadian vaccine trial recruits volunteers

The first test vaccines will be given in the next week or two, and the results will be available to Health Canada and the Public Health Agency of Canada, said Dr. Joanne Langley, a pediatric infectious disease specialist and the principal investigator with the pandemic vaccine clinical trial in Halifax.

It generally takes two to four weeks after the first dose to get results on the antibody levels produced by the vaccine, Langley said. The antibody levels are a sign of the vaccine's effectiveness.

The Canadian trials will test two vaccine formulations: one with an adjuvant, a substance added to boost effectiveness, and one without an adjuvant like the vaccines that will be distributed in the U.S.

"The purpose of the study is to determine whether we need adjuvant or not and what dose of antigen we need," Langley said.

Possible oversupply in Canada

On Monday, Canada's vaccine maker, GlaxoSmithKline, said its first trial results from Germany showed the form of the vaccine containing its AS03 adjuvant is effective after a single dose in adults.

If those findings are confirmed, it could mean Canada will have an oversupply of H1N1 vaccine when it does arrive.

As well, Health Canada has promised 1.2 million doses of adjuvant-free vaccine will be available for pregnant women.

Last week, Dr. David Butler-Jones, Canada's chief public health officer, said Canada plans to roll out the first doses of H1N1 vaccine by mid-November, but could move that date up if a second wave of H1N1 starts sooner.

With files from The Associated Press