At the end of this week, there should enough doses of H1N1 vaccine for 60 per cent of Canada's population. (CBC)

Swine flu activity is down in Canada but federal health officials are cautious about declaring a peak.

Most provinces are seeing fewer hospital admissions and fewer reported cases in schools but the virus still poses a serious health risk, Dr. David Butler-Jones, Canada's chief public health officer, told reporters from Ottawa on Wednesday.

"We are trying to be very careful when using the term 'the peak.' We won't know we have reached a peak in flu activity until we are clearly on the other side of it," he said.

"Passing a peak in activity doesn't mean we decrease our concern. Coming down the mountain is as treacherous as climbing it."

Butler-Jones estimated that one-third of Canadians are immune to H1N1 either because they have been vaccinated or they were infected with the virus.

"Even if you are not personally worried … for the sake of others around you as well as your loved ones, please get your H1N1 flu shot. You'd be doing your part to reduce the risk and level of infection in our communities, and by protecting those around you as well."

To further his point, Butler-Jones discussed how H1N1 is hitting younger people than seasonal flu does.

As of Nov. 21, the median age for hospitalization with H1N1 in Canada is 26, compared with 71 for seasonal flu in 2007-2008. The median age for intensive-care admission is 45, 23 years younger than the median age of 68 seen in the 2007 flu season. Among those who died, the median age for the pandemic virus is 54, compared with a median age of 82 from that earlier flu season.

Children under five have the highest rate of admission to intensive care with this flu, followed by adults 45 to 64, Butler-Jones said.

At the end of this week, there should be enough doses of vaccine delivered to provinces and territories to immunize 60 per cent of the population, said Health Minister Leona Aglukkaq.

Before the new year and perhaps by Christmas, there should be enough vaccine for 75 per cent of the population, Butler-Jones said. The federal government has ordered 50.4 million doses at a cost of $403 million, he told the federal health committee on Wednesday afternoon. It has also invested more than $30 million in marketing its H1N1 message to Canadians on behalf of the provinces and territories, Aglukkaq told the committee.

Once health officials have a firm idea of how many Canadians will take advantage of the vaccine, the government will be able to determine how much it can give to the World Health Organization for developing countries, she said.

This decision will be made in the next few weeks and perhaps in the new year, and in the meantime the priority remains on vaccinating Canadians, Aglukkaq added.