People travel and meet to share festivities over the holiday season. They can also spread infectious diseases. (CBC/Mike Laanela)

The number of new swine flu cases in many communities across Canada appears to be levelling off, federal health officials said Wednesday.

"We say it is levelling off because in most communities, the number of positive tests has fallen and there have been fewer reports of flu outbreaks in schools," Canada's chief public health officer, Dr. David Butler-Jones, told a news conference in Ottawa.

"This is in line with what some Northern Hemisphere countries are seeing. However, in the last few weeks, the number of people with influenza-like illness seeking medical treatment was still four to seven times higher than what is usually seen at this time of year for seasonal flu."

No all-clear has been issued, since H1N1 infections occur in waves and don't hit all areas at the same time.

It's also impossible to tell whether a peak in new infections has occurred until after the fact. In the spring for example, the peak occurred two weeks later than health officials thought because of a delay in reporting cases and hospitalizations, Butler-Jones said.

While 90 per cent of seasonal flu deaths are in seriously ill or elderly people, with H1N1, half of the deaths have been in people under age 50.

For every 100,000 people who don't get the H1N1 vaccine, it's estimated 25,000 will become infected, 25 to 100 will end up in hospital and half a dozen will likely die, Butler-Jones said.

Public health officials in Canada and the U.S. have expressed particular concerns about the coming holiday season. People travel and meet to share festivities, but also, unfortunately, infectious diseases, Butler-Jones said. He reiterated the importance of:

• Washing hands.
• Coughing and sneezing into one's sleeve and not the air.
• Thinking of food poisoning when handling dips.
• Getting vaccinated.

Vaccine distribution

By the end of this week, more than 15 million doses of the H1N1 vaccine will have been distributed to provinces and territories, enough to immunize half the population, Health Minister Leona Aglukkaq said. So far, one-quarter of Canadians — more than eight million people — have received the H1N1 vaccine, she said.

At least three million more doses will be available next week. In most parts of the country, H1N1 shots are available to all, and lineups have dwindled.

There have been 24 cases of confirmed anaphylaxis among people who received the H1N1 shot in Canada. Anaphylaxis is a severe allergic reaction that can cause a person's airways to close up and must be treated quickly with adrenalin, which is available at flu clinics.

Overall, there has been less than one case of severe allergic reaction for every 300,000 doses of vaccine given so far. The exact rate is 0.32 cases per 100,000 doses, Butler-Jones said.

For one lot of vaccine that was withdrawn in provinces last week, the rate was four per 100,000, which is still low but more than the expected one reaction per 100,000 vaccinations, he said. Health Canada and the vaccine manufacturer, GlaxoSmithKline, are investigating.

Of the 172,000 vaccine doses in the recalled lot, all but 15,000 doses had been administered by the time the halt-use order was issued, said Dr. Danielle Grondin, assistant deputy minister of the Public Health Agency of Canada.

There has been one death linked to anaphylaxis. It's not clear exactly what caused the death, which is also being investigated.

Butler-Jones and Aglukkaq credited Canada's intensive surveillance, down to the lot level, compared with other countries that are not so specific.

Mutated strain

As of Tuesday, provinces and territories reported 232 people in hospital and 68 in intensive care with swine flu. The total number of lab-confirmed deaths in Canada since the pandemic began in the spring is 304.

In Ontario alone, 47 people are on ventilators, and doctors are warning people against becoming complacent.

In China, eight more cases of a mutated form of the H1N1 virus have been found.

"These mutations have been seen in a number of countries," Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention said Wednesday.

"We've seen them here in the U.S. and people have seen them in a lot of other countries. They have been associated with severe disease, more often than you would expect by chance alone."

The mutated virus strain has not been reported in Canada, and public health officials said the jury is still out on whether it will be a significant problem.

Meanwhile, fewer outbreaks of other infections seem to be occurring in Canada, Butler-Jones said.

"In Canada, the usual outbreaks that we would see or be tracking we're not seeing — we don't seem to be seeing as many of them. So it may be as we hoped — as we expected — people doing the kinds of things that prevent influenza are also preventing a lot of other infections as well. I think we're all better for it."

With files from The Canadian Press