Tamiflu is one of the few medications believed to be effective against swine flu. Tamiflu is one of the few medications believed to be effective against swine flu. (Ed Wray/Associated Press)

Antiviral medicines should be reserved for Canadians who need them the most, because making the wrong choices could fuel drug resistance, public health experts say.

Federal and provincial stockpiles include 55 million doses of the antiviral drug Tamiflu, also known as oseltamivir, stored in the event of a flu pandemic. Another antiviral, the inhaled drug Relenza, is also effective against the swine flu virus.

Vaccine research

Biotechnology companies in Canada and around the world said Tuesday that they have received a genetic sequence of the new strain of H1N1 swine flu to start working on developing a potential vaccine.

"We have initiated discussions with domestic manufacturers of vaccines to bring them in early," said Dr. Frank Plummer, scientific director general of the National Microbiology Laboratory in Winnipeg. "We are confident that we will be able to get to the point where we have a vaccine seed stock within a few weeks."

The U.S. Centers for Disease Control and Prevention has also taken a sample of the virus to produce a seed stock, the first step in producing a vaccine.

It could take four to six months to develop the first batch of vaccine for public use, the World Health Organization said. Vaccines are produced by growing the virus in eggs and then purifying it, a time-consuming process.

The WHO has not asked vaccine manufacturers to suspend production of seasonal flu vaccines to focus on swine flu. The organization would only take that step if it believes a full-scale pandemic was likely.

Researchers are also testing whether growing vaccines in cells, rather than eggs, could speed up the process.

The antiviral drugs should be used strategically for those at high risk of complications, such as the elderly, said Canada's chief public health officer, Dr. David Butler-Jones.

So far, the swine flu virus is not causing severe illness in Canada or any other country outside of Mexico.

"It's a typical presentation of influenza," Butler-Jones said. "So if you wouldn't be using Tamiflu a year ago, it's not appropriate to use it now."

It's important not to overuse antivirals because the virus could develop resistance to them, he added.

Prevention strategy

The drugs might be needed not only for treatment but also to prevent disease, said microbiologist Dr. Don Low, medical director of Ontario's Public Health Laboratories.

"We probably will also want to use this drug if it does become a pandemic to protect the individuals that are responsible for keeping the infrastructure of our society together, whether it's fire, police, health-care workers, power plant workers," said Low.

So far, lab testing on the swine flu virus shows the stockpiled antivirals would be between 70 to 90 per cent effective in preventing infections.

"There is the debate of whether if a person is given it right away do you contain or stop the spread or slow the spread of it in the community, and that is being determined right now," said Ontario's chief medical officer, Dr. David Williams.

At the Albany Medical Clinic dispensary in Toronto, pharmacist assistant Mike Cooper is down to the last box of Tamiflu.

"We're trying to get it, but it's just hard to find right now," Cooper said. "I think a lot of places are preparing for an outbreak."

For now, it's up to individual doctors to decide who should receive the drugs.