By PHRED DVORAK and BETSY MCKAY

TORONTO — An unpublished Canadian study that suggests getting an annual flu shot may make it easier to contract swine flu has caused most provincial governments in Canada to postpone or limit seasonal-flu vaccination programs.

The study remains a mystery in many ways. It is being reviewed for potential publication in a scientific journal, but the authors won’t say which one. Few people have seen the data, and some experts have expressed skepticism of the results.

The study is co-authored by researchers from the British Columbia Centre for Disease Control, the Ontario Agency for Health Protection and Promotion and Laval University in Quebec.

The World Health Organization isn’t recommending that seasonal-flu vaccinations be postponed. Public-health officials in the U.S., Australia and other countries said their own data doesn’t show such links between seasonal-flu-shot recipients and people who have gotten the new flu strain, known as the 2009 H1N1 flu.

Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, said at a recent news conference that there was no “real explanation technically or scientifically” for an association between the two.

Local governments are taking no chances. Twelve of Canada’s 13 provinces and territories are delaying the rollout of seasonal-flu shots for the bulk of their populations until after their H1N1 inoculations are complete — likely at the end of this year.

The study “wasn’t something we felt we could ignore,” said Perry Kendall, provincial health officer for British Columbia, which like most provinces is limiting seasonal-flu shots to people ages 65 and older until after it has finished its H1N1 vaccinations. “Why would you want to run the risk of doubling peoples’ risk of getting H1N1?” said Dr. Kendall, who noted that he has seen the data and talked to the study’s authors.

The study began after researchers in British Columbia this summer found a possible link between contracting H1N1 and receiving flu shots the previous season, for some people in the province.

The researchers shared the information with colleagues in the other provinces, some of whom in turn found their own links, said Dr. Kendall. Those results were collated into one study covering about 2,000 confirmed cases of H1N1 in places such as British Columbia, Ontario and Quebec. It found that people who got flu shots last year were about twice as likely to contract swine flu as those who weren’t vaccinated, according to sources who have seen the study’s data.

The Public Health Agency of Canada commissioned an international panel of experts to take a look at the study’s methodology; that panel last week said it found no methodological errors and that the study has “merit,” an agency spokeswoman said.

The WHO reviewed the Canadian study and data from other countries in a teleconference late last week with flu experts both inside and outside the agency, including the Canadian researchers involved in the work. “Based on that review, WHO is not issuing any general warning about seasonal-flu vaccine,” spokeswoman Aphaluck Bhatiasevi said.

The WHO’s immunization advisory group will also discuss the study at a meeting at the end of this month, Ms. Bhatiasevi said.

Canada’s local governments said the study was just one factor in their decisions to put off seasonal-flu shots. Provincial health officials said they expect H1N1 to be the dominant flu strain in Canada this winter, as it was in most countries in the Southern Hemisphere during their winter; it thus makes sense to concentrate resources on H1N1 first, they said.

Concurrent inoculations for seasonal flu and H1N1 — as are being given in the U.S. and other countries — would be a logistical nightmare, and it is unclear what will happen if both vaccines are administered at the same time, said British Columbia’s Dr. Kendall. “We don’t know if you can give H1N1 in one arm and another in the other arm,” he says. “Does one vaccine trump the other?”

U.S. public-health officials have said it is safe to get both shots at the same time.

In the U.S., seasonal-flu vaccinations began earlier than usual this year, in hopes of avoiding a crush of simultaneous demand for H1N1 and seasonal-flu vaccines.

Write to Phred Dvorak at •••@••.••• and Betsy McKay at •••@••.•••

Printed in The Wall Street Journal, page A6