Most flu cases are being reported in Alberta, Ontario and Quebec, according to Canada's Public Health Agency, but there is increasing activity in Saskatchewan, Manitoba, and Newfoundland and Labrador.
"We're at or close to peak, certainly in southern Ontario, for influenza activity," said Dr. Doug Sider, medical director of communicable disease prevention and control at Toronto Public Health.
Reported and lab-confirmed cases of the flu in Toronto have already exceeded the previous 10-year average, according to Toronto Public Health.
It's the same situation in Montreal, where the city's two pediatric hospitals are asking parents to keep their children at home if they have mild cold or flu symptoms. Over the past two weeks, the hospitals have received several hundred children with a cold or flu, per day.
"These are record numbers for this time of year," said Dr. Antonio D’Angelo, head of Ste-Justine Hospital's emergency room department.
In Manitoba, the Winnipeg Regional Health Authority said emergency rooms are very busy. According to WHRA's chief nursing officer, the number of people with the flu who are reporting to ERs and could not be sent home is almost double the normal rate for this time of year.
The reason for the high numbers of hospitalizations and activity could be this year's H3N2 flu strain, which is being seen in the majority of cases.
Public health officials said the flu vaccine this year is not as effective in protecting against the H3N2 strain, which tends to cause more deaths and hospitalizations, especially in the elderly.
According to FluWatch, Canada's national surveillance system that monitors the spread of flu, the majority of H3N2 cases have been among individuals 65 and older.
Despite the reduced effectiveness of the vaccine against H3N2, "the vaccine can still provide some protection against H3N2 influenza illness and can offer protection against other influenza strains such as A [H1N1] and B," according to the federal public health agency's website.