Don’t think of the flu as a cold. What to know about H3N2, a fast-spreading, ‘severe viral infection’

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While some may be under the impression that getting the flu is similar to having a cold, a Canadian doctor warns that influenza can lead to serious and even deadly complications.

Dr. Christopher Labos spoke to CTV’s Your Morning Tuesday, following the announcement of the deaths of three children in the Ottawa area from influenza-related complications.

Ottawa Public Health announced Monday that the children, who were between the ages of five and nine, had complications related specifically to influenza A. The deaths came amid warnings across parts of Ontario and Eastern Canada about a higher number of flu cases so far this season.

Labos, a Montreal-based epidemiologist and cardiologist, was asked about these complications, and said “a number of things can start to go wrong” after catching the flu.

“It can progress to a more severe form of pneumonia, where you have a bacterial infection on top of the initial viral infection, the infection can damage your kidneys (and) you can go into renal failure. In older adults, we do see a spike in cardiac disease as a result of influenza,” Labos listed as examples.

These things can be triggered by the virus, he said, “which is why when people refer to the flu as sort of a nothing cold, that is incredibly problematic because influenza is actually a very, very severe viral infection.”

As for the circumstances around the deaths of the children, Dr. Isaac Bogoch told CP24 Tuesday that little is known at this point about any underlying circumstances.

“We know influenza is a very rough virus. We know it can pack a punch. … It sadly kills about 400,000 to 500,000 people per year on the planet. About 2,500 to 3,500 Canadians will succumb to this illness this year,” said Bogoch, a Toronto-based infectious disease specialist.

“And we know it’s most severe in the youngest cohorts, the oldest cohorts, and people who are immunocompromised or have underlying medical conditions.”

Labos said influenza is not one virus but multiple viruses that circulate, and each year, one particular strain can be most dominant.

A common strain this season is H3N2, which Labos says is behind most of the infections doctors are seeing in Canada.

He said this year’s strain seems to be more virulent, or infectious, and causing more severe disease.

Flu watchers got a preview during the summer, when it was winter in the southern hemisphere. Labos said what was seen there is now similar to what has been recently noted in Canada and elsewhere.

Symptoms of influenza, a respiratory infection, typically include fever, shortness of breath, cough and muscle aches, Labos said. In severe cases, patients may require supplemental oxygen.

Recent data from Ontario Public Health suggested that earlier this month, cases were especially high among children aged five to 11. Labos said there are a couple of reasons, one being biology, and the other being the nature of schools.

“We have kids together indoors, breathing the same air for hours a day, in classrooms that are sometimes in older buildings that are poorly ventilated,” he said.

“Kids in school do spread viruses amongst each other. When outbreaks happen, they do tend to happen in this context, and so unless we start investing the money to upgrade the ventilation and putting in air filters in schools, we are going to be having kids getting sick. School is where they spend the majority of their days, so it’s not surprising that you would see infection spreading amongst kids in schools.”

When asked about prevention, Labos said the “most important thing” is getting the flu shot, even though the version of H3N2 in this year’s vaccine is “not a perfect match” for what’s circulating. He said the other strains in the shot do appear to be better matches, and it will still protect against complications and “blunt the impact of the current wave.”

Bogoch made the same recommendation, saying that “it’s not too late” to get the shot this flu season.

Labos also recommended staying home when you’re sick to help protect others, wearing a mask in high-risk settings like mass transit or doctors’ offices, and regular handwashing.

The latest Canadian respiratory virus surveillance update showed the amount of influenza tests which came back positive in the first week of December rose to 20.2 per cent from 13.1 per cent the previous week.

At this point last year, the percentage of positive tests for influenza was 3.1 per cent, and 15 per cent the year before that.

It’s the highest rate seen so far in the 2025-26 flu season, and higher than any positivity rates in 2023-24. It has not surpassed the highest rate in 2024-25, which was in February, based on the published data.

The report warned “indicators of influenza activity are increasing rapidly,” noting most tests were positive for influenza A and specifically H3N2.

Health officials said the number of hospitalizations were increasing, including at pediatric hospitals.