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The 'Canadian Problem': Unpublished data suggest seasonal flu vaccine may increase swine flu risk

September 24, 2009 |  6:30 pm


Canadian researchers have compiled data from British Columbia, Quebec and Ontario that seem to suggest that vaccination against seasonal flu can double the risk of contracting the pandemic H1N1 influenza virus, according to reports in the Canadian Press. The data have not yet been published and the authors refuse to release the information until it is peer-reviewed and appears in a journal, but public health authorities around the world are anxiously looking at results from their own countries to see whether they can confirm or refute it.

So far, no one else had found similar data. That should be a "red flag" that there is something wrong with the findings, experts said. Perhaps there is a statistical problem, a study bias or some other methodological problem that will become apparent only when the paper is subjected to intense analysis.

Meanwhile, the so-called Canadian Problem is causing a hubbub. Some provincial officials in Canada are advocating delaying seasonal flu vaccinations until the data can be corroborated or disproved. Officials elsewhere fear that the news will add to the already widespread -- and largely unwarranted -- fears about the swine flu vaccine and further impair vaccination campaigns.

At a telephone news conference this morning, Dr. Marie-Paul Kieny, director of the World Health Organization's initiative for vaccine research, said that the research team, headed by Dr. Danuta Skowronski of the British Columbia Centre for Disease Control and Dr.Gaston de Serres of Laval University in Quebec, is competent, but that its results are inexplicable.

"Investigators in other countries have looked at their own data ... and none of the other countries have been able to find anything like that," she said. "The reason why this may be different in Canada and in this particular study than in other places in the world is not yet identified."

A spokesman for the U.S. Centers for Disease Control and Prevention said the CDC also had not seen any data like that found in Canada, and the agency continues to recommend vaccination against both seasonal flu and swine flu.

-- Thomas H. Maugh II