An unpublished scientific study is raising questions about whether getting a seasonal flu shot raises the risk of contracting H1N1, but the evidence is unconfirmed and few have actually read the report.

"It appears to be that for people who got seasonal influenza vaccine last year, they were at greater risk of getting H1N1 disease this year," Dr. Donald Low, an infectious diseases expert at Toronto's Mount Sinai Hospital, told CTV News.

The study is based on research in British Columbia, Ontario and Quebec. Health organizations around the world are watching the results carefully, including the U.S. Centers for Disease Control.

"It is difficult to speak about a study that has yet to be published, however, as this is an important issue involving the subject of seasonal influenza and the fast-moving global pandemic of 2009 H1N1 influenza it is important to note the scientists at the Centers for Disease Control and Prevention have not seen this effect in systems we have reviewed in the United States," spokesperson Joe Quimby told The Canadian Press in an email.

The study is still being peer reviewed in an unnamed journal, and it's not clear when it will be published.

It could change how health officials in Canada and around the world plan their responses to a potential swine flu outbreak.

Need for seasonal flu shot questioned

As it stands, it appears that swine flu will likely "crowd out" all other flu viruses this fall, meaning Canadians are more likely to get the H1N1 virus. As such, some health officials wonder if a seasonal flu shot is still necessary.

Is it realistic, they say, to expect Canadians to head to flu clinics twice for two different vaccines, one for seasonal flu and one for swine flu? Young children might even be recommended to get four flu shots, since children usually need two flu vaccinations given a few weeks apart, to give their immature immune systems full protection. This year, they'd need to double up twice.

However, Ontario health officials tell CTV News that the province will provide a seasonal flu vaccination in the next few weeks for anyone aged 65 or older. An announcement is expected Thursday.

Officials also say they will provide H1N1 shots for high-risk groups -- including pregnant women, children and health workers -- in November. Then, the rest of Ontario's population can be vaccinated.

In Quebec, health officials say they're putting the seasonal flu shot program on standby.

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

Delaying the seasonal flu shot program would allow health workers to concentrate on getting swine flu vaccine into the arms of those who most at risk of complications from swine flu.

Another option would be a more limited seasonal flu shot campaign, one that would target seniors and those with weakened immune systems, who are traditionally at highest risk of seasonal flu, but allow younger Canadians to skip it.

A third option would be to scrap the seasonal flu program altogether.

"All that is being studied now. But it should be decided rapidly," White told the Montreal Gazette.

She added that the decision will affect all Canadians: "It's not like Quebec won't vaccinate and Ontario will. It will be a pan-Canadian decision."

Provincial plans

Most provinces had planned to go ahead with their seasonal flu vaccination programs this October, as scheduled. Swine flu vaccination programs likely wouldn't begin until mid-November, the earliest that the vaccine manufacturer will have it ready, tested and approved.

But infectious disease expert Dr. Neil Rau wonders whether having two vaccine programs will confuse patients, who might wonder about which shot they need and which shots they've already gotten. He says holding off on seasonal flu vaccines might be the best way to go.

"I think the people in Quebec are making a good decision because if you start going after seasonal and swine flu all at once, you end up giving -- especially kids -- a huge number of needles," Rau told CTV News Channel Wednesday.

"I have a feeling that all of Canada is going to go this way and maybe other countries will do the same."

Meanwhile, there are still worries that the swine flu vaccination program won't be effective, since the vaccine is expected to arrive at clinics and doctors' offices after the flu's long-discussed "second wave" has already peaked. Swine flu activity is already picking up again in the southern United States and parts of Canada, including Vancouver Island.

And, it's still not certain whether seasonal flu viruses will continue to be "crowded out" by swine flu. While World Health Organization laboratories report they are not receiving many reports of seasonal flu infections, it may be too soon to say whether that will remain the case.

The dilemma of whether to advise Canadians to get two flu shots will likely take care of itself by next year. Flu experts who advise the World Health Organization are now urging vaccine manufacturers in the Southern Hemisphere to drop one of the older strains of flu from the seasonal flu vaccine for next year's winter, to include the new swine flu pandemic H1N1 strain.

Manufacturers in the Northern Hemisphere would likely follow suit, depending on the flu activity by then.

With a report by CTV's Graham Richardson