Flu in Canada: Why are so many kids getting sick?

TORONTO –

The flu has returned with a vengeance after being absent for a number of years during the COVID-19 pandemic. Children are particularly hard hit. Here’s what doctors say is happening, and why.

What strains of flu are we seeing this flu season?

Based on World Health Organization predictions of which strains would emerge, this year’s flu vaccine protects against two influenza A strains — H3N2 and H1N1 — and two influenza B strains, known as the B/Victoria lineage and B/Yamagata lineage .

Right now, H3N2 causes the vast majority of flu cases in Canada. It’s possible the other strains will become more widespread and peak later in the flu season, doctors say.

Over the past decade, influenza B strains have tended to arrive later in the season, Dr. Allison McGeer, infectious disease specialist and microbiologist Consultant at Sinai Health Systems in Toronto.

Does H3N2 make people sicker than the other tribes?

H3N2 can cause more severe disease than other strains, particularly in older people who are more susceptible, in part because it mutates more quickly so people don’t have as much acquired immune protection, McGeer said.

That’s because people build up some protection against H1N1 and influenza B strains throughout their lives, but not against H3N2.

“[For]children who have never had significant exposure to influenza, there isn’t much of a difference in severity between H1N1, H3N2 and B (strains),” McGeer said.

Why are so many children getting sick right now?

Flu season started early this year, doctors say, meaning kids were getting sick earlier. And COVID-19 safety measures like covering up have also kept other viruses like the flu at bay for the last two cold and flu seasons.

“We are now seeing all of our old viral foes playing again after a hiatus of a few years,” said Dr. Justin Penner, Pediatric Infectious Disease Specialist at Children’s Hospital of Eastern Ontario and member of the Canadian Pediatric Society Committee on Infectious Diseases and Vaccinations.

Children under the age of five are at the highest risk of getting seriously ill with the flu, doctors say. And because of the precautionary measures taken for the COVID-19 pandemic, the immune systems of many children under the age of three have not yet come into contact with the virus.

“Children between the ages of zero and three have about a 40 percent chance of getting the flu in any given year,” McGeer said.

“We now have about two and a half cohorts of children who have not been exposed to influenza at all. So they all get sick at the same time.”

Why do some people end up in the hospital with the flu?

In the vast majority of cases, the flu can be treated at home, doctors say.

But like many diseases, some cases become more serious, McGeer said.

“There’s a whole range (of reasons) from the severity of the influenza illness itself to complications,” she said.

For example, some flu patients might get pneumonia or a bacterial infection along with the virus.

Myocarditis and encephalitis are other possible complications of the flu.

People with weakened immune systems may also be at higher risk of serious illnesses.

“Influenza can also trigger exacerbations of the underlying disease,” McGeer said, including heart disease and stroke.

Seniors are also more vulnerable to being hospitalized with the flu, but a higher risk in the elderly age group appears to be offset by public health measures like continued masking in care homes this year, she said.

Why are so many people reluctant to get vaccinated against the flu?

The Public Health Agency of Canada says it aims to reach an 80 percent flu vaccination rate by 2025, but uptake falls far short of that every year.

The influenza vaccine has a “bad reputation” for being effective but not perfect, Dr. James Kellner, pediatric infectious disease specialist and epidemiologist at the University of Calgary.

Based on data from Australia, which has already had its flu season, this year’s vaccine appears to be about 50 percent effective in reducing severe flu illnesses, he said.

That’s a difference people tend to underestimate, Kellner said.

“If you look at 50 percent prevention of major episodes, it certainly could have saved (this year) a lot of misery across the country.”

The fact that flu shots are required every year instead of a one-time shot also puts some people off, he said.

Also, “there’s so much fatigue” for COVID-19 public health responses, Kellner said.

“The initial reception of the COVID vaccine was so successful for a variety of reasons, but a big part of it was that there was this sense of community in the collective willingness and desire to do the right thing,” he said.

“It seems we just kind of lost that.”

Many people also don’t take the flu seriously enough or realize how severe it can be, especially for young children, Kellner said.

“There’s a feeling that the flu vaccine isn’t that important and so a lot is missed.”

Some people also mistakenly believe they got the flu even though they’ve been vaccinated, said Penner of the Canadian Pediatric Society.

“People’s perception of what influenza or flu is could be a variety of different viruses,” he said.

When people get the flu despite being vaccinated, the vaccine can make the disease less severe, Penner said.

How can we protect ourselves and our families?

Experts say the most effective measures to protect against the flu are:

– Get the flu shot. Doctors say it’s not too late.

– Stay home if you feel unwell

– masking

– Frequent hand washing

This report from The Canadian Press was first published on December 16, 2022.

Canadian Press health reporting is supported by a partnership with the Canadian Medical Association. CP is solely responsible for this content.