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TORONTO - In the face of concerns that swine flu may mount a fall surge, public health officials in Canada are rethinking pandemic and seasonal flu vaccination plans, with issues of timing and vaccine formulation back on the table, a variety of on- and off-the-record sources say.

The pros and cons of a number of scenarios are being hashed out, including delaying, cutting back or cancelling the seasonal flu shot effort and maybe even rethinking the decision to use an adjuvant in the formulation of the pandemic vaccine.

The hope is to get a consensus, so that provinces and territories use the same strategy, officials in Quebec and Ontario have said.

"We're trying to get a pan-Canadian approach here," said David Jensen, a spokesperson for the Ministry of Health and Long-Term Care in Ontario.

While the details are being worked out, Quebec says it will not start rolling out its seasonal flu shot program.

"For the moment, it's on hold," said Karine White, a media relations liaison with the Ministry of Health and Social Services in Quebec.

Up till now the plan has been for provinces and territories to run their seasonal flu shot programs first, starting essentially any time now. They would be followed up with pandemic vaccination efforts after swine flu vaccine is licensed for use in early-to-mid November. Those plans anticipated that the pandemic virus might follow the pattern of seasonal flu, with a second wave hitting in the winter. But swine flu activity is already picking up in the United States and parts of Canada, including British Columbia, are seeing an uptick of cases.

The fear is that the wave may crest before pandemic vaccine is ready, or at least that vaccine will arrive too late to make a difference. Meanwhile, it's not clear whether seasonal influenza A viruses will reappear this winter and if they do how much disease they will cause.

"It doesn't make sense to be putting a lot of effort into delivering seasonal vaccine when the threat is something else that it's not going to protect against," said Dr. David Scheifele, director of the vaccine evaluation centre at B.C. Children's Hospital in Vancouver.

In previous pandemics, the new influenza A virus has replaced the influenza A virus that preceded it. While World Health Organization laboratories report they aren't finding many seasonal flu viruses, it's too soon to say if replacement of both the seasonal influenza A viruses will occur this time around.

And one can never predict how big a role influenza B viruses - which aren't vulnerable to the replacement phenomenon - will play in any given flu season.

White said Quebec is looking at a range of options. The seasonal vaccine could be given as usual or delayed until after the pandemic vaccination effort has been completed. Or a more limited seasonal shot campaign might be undertaken, one that would target people like seniors who would be at highest risk if seasonal flu viruses do circulate.

Another option she mentioned is cancelling seasonal flu shots altogether.

"All of these scenarios are on the table," White said from Quebec City.

But Scheifele and others believe it is premature to decide to junk the seasonal campaign, though the idea of a delayed and more targeted delivery of seasonal flu shots makes sense to some experts.

"We're not anticipating that the seasonal viruses will be circulating while the pandemic is unfolding. It pretty well crowds out the other viruses," Scheifele said.

"The concern is if the pandemic wave is over by Christmas, then there's still a lot of cold winter left for the other seasonal agents to return. If that's the case, then one could revisit the distribution of seasonal vaccines or simply pick up that thread in January."

Dr. Michael Gardam of the Ontario Agency for Health Protection and Promotion agrees it's an idea that is worth exploring.

"Looking at what's happened in the south (Southern Hemisphere) versus what we're having now versus the tendency of pandemic viruses to replace seasonal strains, it is very reasonable to have that discussion," said Gardam, the agency's director of infectious diseases prevention and control.

Another issue that appears to be on the table is the proposed use of an adjuvant in the pandemic vaccine. Adjuvants are additives that boost the impact of a vaccine, allowing a smaller dose to be used for each person.

Canada has said it will buy adjuvanted vaccine from GlaxoSmithKline, which has the country's pandemic vaccine production contract. GSK is making the vaccine at its facility in Ste-Foy, Que.

GSK plans to sell the vaccine in 3.75 microgram doses with adjuvant, a quarter of the size of the non-adjuvanted doses the United States will get from its pandemic vaccine suppliers.

While adjuvants have been used for years in Europe in flu vaccine targeted at seniors, there is no licensed flu vaccine containing adjuvant in this country.