OTTAWA, Sept. 23 (Xinhua) -- Preliminary results from some studies have found that seasonal flu shot may increase the risk of catching A/H1N1 flu, Canadian scientists said Wednesday.

    About 2,000 people from four Canadian provinces were involved in the separate studies, which showed that people who had received the seasonal flu vaccine in the past were more likely to get sick with the H1N1 virus, the Canadian Broadcasting Corporation (CBC) said in a report Wednesday.

    Researchers know that, theoretically, when people are exposed to bacteria or a virus, it can stimulate the immune system to create antibodies that facilitate the entry of another strain of the virus. Dengue fever is one example, scientists say.

    But experts stressed that these are very preliminary results and need to be validated.

    "This is some evidence that has been floated; it hasn't been validated yet, it's very preliminary," cautioned Dr. Don Low, microbiologist in chief at Mount Sinai Hospital in Toronto.

    But these are nevertheless very important data to help guide policy decision, as the time comes for seasonal flu shot, he said.

    This latest finding raises questions about the order in which to get flu shots. Across Canada, public health authorities are fiercely debating the idea of shortening, delaying or scrapping their seasonal flu vaccination campaign in favor of mass inoculation against A/H1N1.

    The main reason is because A/H1N1 may be the dominant strain of influenza circulating when the fall flu season hits, meaning it could be a waste of time and resources to mount a seasonal flu vaccine campaign.

Special Report:  World Tackles A/H1N1 Flu