TORONTO — The Public Health Agency of Canada is rolling out its first doses of unadjuvanted H1N1 flu vaccine this week, a move that should offer relief to pregnant women unwilling to bare their arms for the adjuvanted shot.

The agency has already begun delivering vaccine without an adjuvant to the provinces and territories and plans to have dispersed almost 225,000 doses by week's end.

An adjuvant is a substance added to a vaccine to improve the immune response. A dose of vaccine with adjuvant uses one-quarter of the amount of antigen (the material that induces an immune response) used in a shot made without such a boosting additive.

The World Health Organization had earlier advised pregnant women - especially those in the first trimester - to get unadjuvanted vaccine if available because of a lack of safety data for that population.

Based on that advice and public concern, Canada ordered two million doses of unadjuvanted vaccine, including 200,000 doses recently purchased from Australia. (Pregnant women who contract H1N1 flu are at an elevated risk for serious complications.)

But on Friday, an expert committee that advises the WHO said H1N1 flu vaccines containing adjuvant and vaccines without the additive appear to be equally safe, so there is no need to recommend that pregnant women get the latter version.

Still, that may not allay concerns for some pregnant women who have decided they want the adjuvant-free version of the vaccine no matter what.

And now that adjuvant-free vaccine is available in Canada, just how will it be delivered to those pregnant women who want it?

So far, there doesn't seem to be a clear answer.

Dr. Vita Senikas of the Society for Obstetricians and Gynaecologists of Canada (SOGC) said the professional organization has no plans to have its members inoculate pregnant women in their offices.

The reason is to avoid wasting any "precious vaccine," which comes in vials of 10 doses and can only be stored for a short time, she said Monday from Ottawa.

"You can appreciate that if the health-care provider sees only, let's say, that particular day three pregnancies, what are you going to do with the other seven shots that you can give from the vial?"

But Dr. Perry Kendall, B.C.'s chief health officer, said when the province receives its first delivery of 25,000 doses of unadjuvanted H1N1 flu vaccine, it will not be restricted only to those who put out their arms at mass vaccination clinics.

"I think it will probably be Ob-gyns, family doctors and midwives in British Columbia," Kendall said from Vancouver. "We'll be trying to figure out who has got the patients and how many so we can make a targeted distribution."

The Ontario government has already received its first quota of unadjuvanted vaccine, and was to begin shipping the 86,800 doses to health units across the province on Tuesday.

"It will take one to three days for all the health units to receive their shipment," said Dr. Arlene King, Ontario's chief medical officer of health.

"It will be a mixed-delivery system in the province again for that program," said King, noting that discussions are ongoing as to where pregnant women will be able to access the immunization besides mass-vaccination centres.

"This will be a decision made at the local health unit level in terms of how to best deliver the 86,800 doses of unadjuvanted vaccine that we're getting," she said. "I do not want pregnant women waiting in long lines, so however we can best enable access to pregnant women to this new vaccine, we will implement that."

Manitoba has also received its initial allocation, 9,200 doses that will be distributed to the province's regional and First Nations health authorities based on per capita pregnancy rates, said Gerry Delorme, director of the Office for Disaster Management at Manitoba Health.

"Initially, since we have limited supply, we're going to be using mass vaccination, but that will change as more supply comes into the province," he said from Winnipeg. "As more vaccine comes, we're going to be partnering with the physicians in the communities that work with these women to make sure it is available."

Given the unexpectedly huge public uptake of the adjuvanted vaccine - and numerous examples of how the distribution system has gone awry - some updated information may need to go to vaccinators along with the adjuvant-free version.

For instance, a Toronto-area woman who was 19 weeks' pregnant wrote to a newspaper that she had waited with her toddler for six hours to get her shot with adjuvanted vaccine. When she reached the front of the line, the woman was told she would have to wait until she was 21 weeks' pregnant or until unadjuvanted product became available.

"It's not the first refusal that we've heard of, of a pregnant women who has showed up," said Senikas, explaining that caution about giving a woman less than 20 weeks' pregnant the adjuvanted shot is based on a "theoretical precautionary risk."

"In an area where there happens to be pandemic activity or someone has an underlying (medical) condition, whatever vaccine is available for a pregnant women under 20 weeks - get it," she advised. "By all means, get whatever vaccine is available."

Meanwhile, initial results from a U.S. study of 120 healthy pregnant women showed they mounted a robust immune response following just one dose of H1N1 flu vaccine, an unadjuvanted product made by Sanofi Pasteur in its plant in Swiftwater, Pa.

"For pregnant women, who are among the most vulnerable to serious health problems from 2009 H1N1 infection, these initial results are very reassuring," said Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, which sponsored the trial.

"Importantly, the pregnant women participating in the trial have tolerated the vaccine well and no safety concerns have arisen."