This year's flu shots include the H1N1 and H3N2 strains. (CBC)

Central Canada is probably starting to hit the peak of a flu season that started earlier than normal and is causing more severe disease in the elderly, doctors say.

Although last year's H1N1 strain primarily affected younger Canadians, the H3N2 strain is causing large outbreaks in nursing homes where residents are more likely to end up in hospital and intensive care.

"We've seen really a burst of activity [around Toronto] that came between the holiday seasons, which has continued over the last two weeks," Dr. Don Low, medical director of Ontario's public health laboratories, said Friday.

"We're probably starting to hit the peak of this new influenza season."

Last year, people were being vaccinated against H1N1, not H3N2.

When there is a larger population susceptible, it is more likely that a virus will be transmitted from person to person, Low noted.

Along with vaccination rates, conditions such as the temperature, absolute humidity, how crowded people are and underlying immunity all make a difference in flu spread, health officials said.

The number of confirmed flu cases in Ontario is six times higher than the average for early January, according to the province's health ministry.

Hospital seeks more beds

Toronto, Montreal and the areas surrounding those cities seem to be particularly hard hit, said Dr. Michael Gardam, chief infection control officer at Toronto's University Health Network.

"I've been doing this work for 13 years, and the last four weeks, I’ve seen more flu in our hospital than I’ve ever seen before," Gardam said in an interview.

The hospital network has had to open previously closed bed and reallocate beds from surgery to medicine to allow more patients to be admitted, Gardam said.

The Public Health Agency of Canada's FluWatch map up to Jan. 8 showed widespread activity in southeastern Quebec.

"Although the percentage of specimens testing positive for influenza increased slightly in week 01, the national rate appears to be approaching the peak," the agency said Friday.

Ontario's Health Ministry is urging people who are especially vulnerable in particular — the elderly, young children, pregnant women and people with weakened immune systems — to get free flu shots.

In the U.S., four states — Alabama, Georgia, Louisiana and Mississippi — had high levels of flu activity for the week ending Jan. 8, the U.S. Centers for Disease Control and Prevention said. That is down from six states the previous week.

In Britain, the number of flu deaths between Jan. 6 and Jan. 13 was 112, up from 50 in the previous seven-day period. Of the most recent fatalities, 95 involved the H1N1 flu strain, according to figures from the Health Protection Agency. Most of the deaths occurred among people age 65 and older.

"Some indicators are suggesting that the level of flu activity is beginning to plateau but this should be interpreted with caution as we are still monitoring data collected over the Christmas and New Year period when the rate of consultations will have been lower due to closure of school and GP surgeries," the Health Protection Agency said.

British health officials are seeing Strep A and other secondary infections piggybacking on the flu virus, the CBC's Ann MacMillan said.

The same hasn't been observed in Canada, but it may still be too early in the season, Low said. Such secondary infections typically occur about six to eight days after the flu, he said.