10/17/2009 01:13 pm ET Updated Nov 17, 2011

'The Canada Problem': Could a Seasonal Flu Shot Help Spread Swine Flu?

Just as Americans balance fears of various strains of influenza with concerns about how vaccines for seasonal flu and swine flu might affect them, the medical world has been vexed by "the Canada Problem:" A Canadian study has concluded that people under the age of 50 vaccinated for seasonal flu are twice as likely to catch swine flu.

The study, which assessed results obtained by 2,000 Canadians in three big provinces, has not been published. Its authors say it is undergoing pre-publication peer review at a scientific journal--an academic formality scorned by The Globe & Mail in an editorial demanding the paper be published.

The newspaper noted that most Canadian provinces have revised their seasonal vaccination plans to inject only the elderly and residents of long-term care facilities until after the country's swine flu vaccines have been rolled out in November. Then it thundered: "Momentous decision are being made, but the public is being denied access to the basis for those decisions."

The study was the subject of a high-level global teleconference held by the World Health Organization. As detailed in a report by Helen Branswell--the world's top flu reporter--authorities have decided to proceed with seasonal flu vaccinations everywhere but in Canada on the assumption that the study is somehow flawed.

A prime problem is that no other health body or researcher has found a link between seasonal flu vaccine exposure and greater likelihood of catching swine flu. (A study in the British Medical Journal found the opposite effect, but tracked only 60 Mexican patients.)

Count the U.S. Centers for Disease Control unimpressed. "We have not seen such evidence in cases here in the U.S. and we recommend seasonal and H1N1 vaccination in those groups recommended to receive them," said a spokesman.