Canada is cracking down on the growing number of Americans who are scrambling to get flu shots inCanada as the anxiety over a shortage of vaccine in the United States spreads, it is reported Saturday.

    With half of the US supply choked off by quality-control problems, clinics such as the border outpost of the Northwestern Health Unit in Fort Frances, Ontario Province, have been getting asteady steam of calls from worried Americans.

    On Wednesday, Ontario Health Ministry officials held a conference call with the province´s 37 public health officers and instructed them to start demanding proof of Ontario residency before giving anyone the shot.

    Canada´s western province of Alberta has taken similar precautions, restricting access to free flu shots to residents of the province as a "strictly short-term measure" during the supply shortage in the United States, said John Tuckwell, a spokesman forAlberta Health and Wellness.

    Albert Schumacher, president of the Canadian Medical Association, also warned doctors Friday to avoid giving US visitors any of the vaccines purchased by provincial health plans,which represents the vast majority of the supply in Canada.

    The US shortage of flu vaccine was caused by the decision of British regulators to shut down a drug manufacturing plant in Liverpool, citing concerns about possible contamination. That factory was supposed to supply almost half of the 100 million flu vaccine doses expected to be administered in the United States this season. Canada´s vaccines come from a different manufacturer.