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Flu season has officially started in Canada, public health agency says

The dominant strain now will be influenza A type H1N1, says an infectious diseases specialist
The Public Health Agency of Canada said Friday that the flu season is officially underway in this country. Needles and syringes used to administer the flu shot are pictured on Monday, October 5, 2020. THE CANADIAN PRESS/Tara Walton

Flu season has officially begun in Canada, the federal public health agency said on Friday.

“At the national level, influenza activity has crossed the seasonal threshold, indicating the start of influenza season,” the Public Health Agency of Canada said in its weekly FluWatch report posted online.

The rate of tests that were positive for flu stayed above five per cent for two consecutive weeks.

As of Nov. 25, 7.5 per cent of people tested for influenza across Canada were positive.

The number of cases is climbing, said Dr. Allison McGeer, an infectious diseases specialist at Mount Sinai Hospital in Toronto.

“If you plan to get a flu vaccine, now is a really good time to do it,” she said in an interview.

“The flu season starting now tells you that there’s going to be a lot of flu at the end of December and the beginning of January,” McGeer said, noting the flu shot takes about two weeks to prime people’s immune systems.

“That’s when you want to be out with your friends and doing a bunch of things and, you know, flu is capable of making that time quite miserable.”

Not all provinces and territories are reporting a five per cent positivity rate yet. For example, Public Health Ontario’s latest flu surveillance report said the rate was 2.8 per cent as of Nov. 25 in that province.

But Ontario and other provinces will soon catch up and those rates will increase, McGeer said.

The dominant strain now will be influenza A type H1N1, which is a good match for the current vaccine, she said.

Many adults have some level of resistance to H1N1 flu strains, so it “tends to cause a lot of disease in kids, especially unvaccinated kids,” McGeer said.

She added that “emergency departments and pediatrics … take more of the pressure” during H1N1-dominant flu seasons.

Although McGeer said it’s important for people to get their flu vaccines, she’s even more concerned about the levels of COVID-19 that are circulating this year.

Friday’s surveillance report from Public Health Ontario showed a test positivity rate of 20 per cent for COVID-19 in that province.

In addition to test positivity, wastewater surveillance and hospitalizations show climbing COVID-19 cases in Canada, McGeer said.

“Just because we’ve stopped talking about people being hospitalized with COVID does not mean that people aren’t being hospitalized with COVID,” she said.

“At the rate we’re going, there will be more people hospitalized with COVID and more people dying from COVID this year than last year,” McGeer said, noting that a low uptake of the new COVID XBB-variant vaccine is worrisome.

This report by The Canadian Press was first published Dec. 1, 2023.

Nicole Ireland, The Canadian Press