Until now, the plan has been for provinces and territories to run their seasonal flu shot programs first, followed by swine flu vaccine shots. (John Amis/Associated Press)

Canadians could have clearer guidelines about the timing of pandemic and seasonal flu vaccinations by the end of the week, a health official in Ontario said Wednesday.

Health authorities in Quebec say they might scrap or delay seasonal flu shots and carry out mass vaccinations against just the H1N1 swine flu virus instead. In the meantime, the province has paused the launch of its seasonal flu shots.

Federal, provincial and territorial health officials are aiming for a pan-Canadian approach to flu vaccinations. Until now, the plan had been to offer seasonal flu shots first starting soon, followed by pandemic vaccinations after the swine flu vaccine is licensed for general use in early to mid-November.

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

"My advice right now is definitely stay tuned," said Dr. Michael Gardam, director of infectious diseases prevention and control at the Ontario Agency for Health Protection and Promotion.

Seasonal shots for seniors?

"We are working on this as we speak, and I think there will be very clear messaging on this even within the next couple days to really help people decide," he added in an interview with CBC Newsworld.

"You can imagine the people over the age 65 who are relatively protected against H1N1, it may make perfect sense for them to get the seasonal vaccine. People who are younger than that, if we don't see a lot of seasonal flu, probably the pandemic vaccine's the way to go. But we're going to make that crystal clear to people."

Gardam pointed to the Southern Hemisphere, where the H1N1 strain overtook seasonal flu strains to become the dominant one circulating.

That raises the question of why a seasonal flu shot campaign should be mounted if an outbreak isn't expected. But an initial bump of pandemic flu could be followed by the seasonal flu.

"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," said Dr. David Scheifele, director of the vaccine evaluation centre at B.C. Children's Hospital in Vancouver.

"If that's the case, then one could revisit the distribution of seasonal vaccines or simply pick up that thread in January."

All options on table in Quebec

Epidemiological studies are also underway to test whether one vaccine cancels out the efficacy of the other and to tease out which one may cause side-effects if both shots are given around the same time.

In previous pandemics, the new influenza A virus replaced seasonal influenza A viruses, but it's too early to tell if this will also occur now.

White said Quebec is considering all options, namely:

• Giving seasonal vaccine as usual.
• Delaying seasonal flu shots until after the pandemic vaccine is delivered.
• Scaling back the seasonal flu campaign to focus on those at highest risk of those strains, such as seniors.
• Cancelling seasonal flu shots.

No adjuvant?

Health authorities are also debating the proposed use of an adjuvant in the pandemic shots, which boosts the effectiveness of the vaccine so a lower dose of the active ingredient can be used.

Canada's seasonal and pandemic flu vaccine contract is with GlaxoSmithKline, which makes the vaccines at its facility in Quebec City.

GSK plans to sell H1N1 vaccine that includes 3.75 microgram doses with adjuvant — 25 per cent of the size of the doses the United States is buying from pandemic vaccine suppliers that are not using adjuvants.

The federal government has ordered 50.4 million doses of vaccine, most of which will contain an adjuvant. About 1.2 million doses have been set aside that won't include the adjvuant and are intended for pregnant women. Little research has been done on the effect the adjuvant could have on them.

Other unresolved questions include whether an adjuvant is needed at all, given that studies so far suggest the H1N1 vaccines without the adjuvant seem to protect adults, and whether Canada could change its contract with GSK at this point.

With files from The Canadian Press