TORONTO - Delivery of H1N1 vaccine to the provinces will slow a bit over the next couple of weeks because the country's vaccine manufacturer was asked to make special batches of product for pregnant women, Canada's Chief Public Health Officer said Thursday.

Dr. David Butler-Jones said at this point he couldn't predict how much vaccine will flow to provinces over the next two weeks. But he said the slowing of the flow would likely require some to scale back their vaccination efforts.

“We're still working that out. It's a very fluid situation,” he said in an interview.

“I know some (provincial authorities) are thinking at the point that at least for next week they'll need to cancel some of their clinics.”

The word comes amid massive lineups at clinics as people scurry to get vaccinated against a virus now causing disease in many parts of the country.

“The response in the first week has been quite overwhelming and we obviously appreciate people's patience,” Butler-Jones said.

“In the next couple of weeks if people who are at low risk of severe disease could just wait a couple of weeks, the lines might be better and it will mean it (the vaccine) can be focused on those at greater risk.”

Butler-Jones estimated deliveries for the next two weeks would be below the two million doses a week the vaccine manufacturer, GlaxoSmithKline, has been producing for the past few weeks.

At this point, federal authorities had hoped GSK would be putting out three million doses a week but Butler-Jones said output should reach that level after this temporary shutdown.

The three northern territorities, which have unique delivery challenges, have all received their entire allotments of vaccine. Vaccinators there have to crisscross vast swaths of terrain by airplane, flying in to conduct flu shot clinics then flying on to the next community.

Butler-Jones said that by the end of this week six million doses will have gone out across the country.

That's nearly enough to cover the people identified as being in the priority groups for first access to vaccine, estimated at between seven and eight million people, he said.

Priority groups include health-care workers, pregnant women, young children, adults younger than 65 with chronic diseases and residents of remote communities.

The slowdown in the flow of vaccine is due to the fact that Canada asked GSK to make special batches of vaccine for pregnant women and that required switching over the production line, and then switching back.

Based on advice from the World Health Organization, federal authorities decided to offer adjuvant-free vaccine to pregnant women.

Adjuvants are compounds that boost the immune response to vaccine, allowing lower doses to be used. While tens of millions of doses of adjuvanted vaccine have been given - mainly in Europe - there are no data on its use in pregnant women.

As a result, the WHO suggested countries that had the option should offer pregnant women unadjuvanted vaccine.

By next week about 225,000 doses of unadjuvanted vaccine will have been sent out to provinces, Butler-Jones said.

He suggested the country is still on target to have enough vaccine for every Canadian who wants to be vaccinated by Christmas.