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The antiviral drug Tamiflu shouldn't be used to prevent H1N1 infection in people exposed to the virus but not sickened by it, WHO says. ((Sang Tan/Associated Press))

Provinces and territories appear to have no standard approach to flu vaccinations as they examine preliminary research suggesting people who have had seasonal flu shots might be at greater risk of catching swine flu.

Ontario's chief medical officer of health announced a three-pronged approach to flu vaccination in the province Thursday:

  • Seasonal flu vaccinations for people older than 65 and residents of long-term care homes will take place in October, since those groups are considered to be at greater risk from that flu than from swine flu.
  • A wider swine flu vaccination campaign for the rest of the population starting in November, when a vaccine becomes available against the H1N1 influenza A virus, the swine flu strain that has been spreading worldwide since April.
  • Seasonal flu vaccinations for people younger than 65 —  but only after the H1N1 shots have been given.

A similar approach in delaying seasonal flu vaccinations has been adopted by Quebec, which will hold off seasonal shots until January, as well as by Saskatchewan and Nova Scotia. Other provinces, including  British Columbia, are also considering it.

But New Brunswick hopes to complete its seasonal vaccination program by mid-October, instead of offering the shots in November as in previous years. 

Newfoundland and Labrador has recommended the seasonal flu shot be given out starting in October to anyone over the age of 65, residents of long-term care homes and adults and children with chronic heart or lung disease. The province plans to offer swine flu shots starting in November, or earlier if deemed necessary.

Other provinces and territories haven't formally announced their flu shot plans yet.

Call for national approach

Most provinces and territories have been reviewing their vaccination plans since Canadian researchers found people who had received the seasonal flu vaccine in the past were twice as likely to get  the H1N1 virus. The research has not yet been peer-reviewed or published. 

Tamiflu resistance

The World Health Organization put out new guidelines Friday recommending against using the antiviral drug Tamiflu, also called oseltamivir, to prevent H1N1 infection in people exposed to the virus but not sickened by it.

"The risk of resistance is … considered higher in people who receive oseltamivir for so-called 'post-exposure prophylaxis' following exposure to another person with influenza and who then develop illness despite taking oseltamivir," the UN agency said.

Of 28 cases of Tamiflu-resistant flu, 12 were related to prophylactic or preventive use. 

The number of Tamiflu-resistant cases remains "sporadic and infrequent," WHO said.

Theoretically, antibodies created by the immune system after exposure to bacteria or a virus can facilitate the entry of another strain of the virus or disease. The effect has been seen for other viral vaccinations but never for influenza, said Dr. Donald Low, chief microbiologist at Mount Sinai Hospital in Toronto.

"I think it's a reason that it would be great to have a national policy on this because we're now hearing messages from different provinces about different approaches to this issue with these new results that have come out," Low said Friday.

"That is also going to confuse individuals," especially since the research finds are confusing to doctors and medical researchers as well, he said.

Dr. David Butler-Jones, Canada's chief public health officer, said people should follow vaccination advice from their provincial and territorial medical officers of health.

"I'm not worried about the seasonal vaccine," he told reporters.

The head of the U.S. Centers for Disease Control said Friday his agency would love to see Canadian data that appear to link getting a seasonal flu shot with catching swine flu.

U.S. data don't suggest that the seasonal flu vaccine "has any impact on the likelihood of getting H1N1," Dr. Thomas Frieden said. He has ordered his own scientists to review the findings.

Meanwhile, the CDC is recommending that vaccinations for both seasonal and H1N1 flu go ahead as quickly as possible.

Butler-Jones noted that the Canadian government has purchased 600,000 more doses of H1N1 vaccine that does not include an adjuvant, a substance used to boost immune response.

About 1.8 million doses will be offered to pregnant women and children under the age of three, since there is little clinical data on the safety and effectiveness of the adjuvant in those two groups.

As of Thursday, there were 78 deaths in Canada among people with confirmed H1N1, up by two since Sept. 12. There were also 15 people in hospital and three admissions to intensive-care units in that time, Health Minister Leona Aglukkaq told reporters.

With files from The Canadian Press