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Only some people get tested when they seek medical care, so positive case rates are "the tip of the iceberg" when it comes to how much flu is actually circulating, said Dr. Jesse Papenburg, an infectious disease specialist at Montreal Children's Hospital. 

A lot of kids with flu symptoms are coming to his emergency department and the number of children admitted to hospital has been increasing over the past few weeks, he said, noting that some children have had to go to the intensive care unit. 

Children under six years of age, seniors, people with chronic health conditions and people who are pregnant are at the highest risk of becoming severely ill from the flu or suffering complications, the PHAC website says.  

�We are clearly in the thick of a rather intense influenza season,� said Papenburg, who is also an assistant professor of pediatrics at McGill University. 

Although it varies from year to year, the flu season usually begins in November or early December. But this year, it didn't really get "kick started" until after the holidays, he said. 

"That's when you saw also in Quebec the test positivity rate really starting to have a sharp incline," Papenburg said. The province has the highest positivity rate in the country at 32.1 per cent, according to PHAC data.

The data also show positivity rates in the territories have climbed to 29.8 per cent, with B.C. at 28 per cent. The next highest reported positivity rate is in Ontario at 19.8 per cent. 

The latest influenza test positivity rates were published on PHAC's website on Thursday afternoon. The national rate of 24.3 per cent is double the 12.1-per-cent positivity rate found at the same time last year.    

Dr. Allison McGeer, an infectious disease specialist at Mount Sinai Hospital in Toronto who researches influenza epidemiology, said this is "an odd year" for flu. 

Influenza A strains H3N2 and H1N1 always circulate, but one of them usually dominates, McGeer said. In a "mixed season" where both strains have high levels of activity, there tends to be a peak of one strain followed by a peak of the other, she said. 

But this year, a lot of both H3N2 and H1N1 activity is happening at the same time, McGeer said. 

Papenburg said this could be a key reason why this flu season is worse than usual. 

"It's kind of like there are two outbreaks or two epidemics … occurring at the same time of two different strains of influenza A," he said. 

According to the U.S. Centers for Disease Control and Prevention website, the southern hemisphere's flu season earlier this year saw either H3N2 or H1N1 dominate in various countries — not both. 

The influenza B virus is also present in Canada at a much smaller level right now, but tends to increase later in the flu season, infectious disease experts say. 

Papenburg urged people who did not get a flu vaccine this fall or winter to get their shot, noting that high levels of influenza A could continue for a few more weeks and that influenza B "is starting to creep up as well." 

Although the shots may not prevent people from getting the flu, they reduce the risk of getting so sick that medical attention is required by about half, he said.  

McGeer recommended people also use other measures to protect themselves against the flu, including handwashing and wearing a mask in indoor crowded places. 

While flu is on the rise, two other respiratory viruses — COVID-19 and respiratory syncytial virus (RSV) — are declining in most of Canada, according to the latest PHAC data. 

The exception is in Atlantic Canada, where RSV cases have increased with a test positivity rate of 13 per cent in the week ending Feb. 8. 

This report by °µÍø½ûÇø was first published Feb. 14, 2025.

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