While health officials had their hands full in 2014-15 with a nasty H3N2 flu season, Canadians have managed to stave off influenza so far this year. Doctors and infectious disease experts are pointing to a handful of reasons why.
“We have very sporadic activity across Canada. It’s really not here at all,” Jason Tetro, a Canadian microbiologist and author of the new book, The Germ Files, told Global News.
“We just haven’t had a bad season and the answer as to why is multi-factoral,” according to Dr. Michael Gardam. He’s the director of infection prevention and control at the University Health Network in Toronto.
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There’s the warm weather, a vaccine that covers this year’s bases, and last year’s nasty strain that already took its toll. Here’s why experts say this year’s flu season has been nearly non-existent.
We’re experiencing a warmer than normal winter: Across the country, temperatures have been above normal this winter thanks to El Nino. A balmy December does not bode well for influenza, which thrives on people snuggling up and spreading germs indoors.
“The flu is not based on the calendar, it’s based on climate. As a result of that, if it’s warmer, there’s a less likelihood that you’ll see the flu spreading around,” Tetro explained.
“The only way the flu spreads is basically by having people within six feet of each other, coughing and sneezing,” he said.
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Across the board, other respiratory illnesses that come along with the winter season have been tame, too, Gardam says.
“It’s predictably unpredictable. If this nice weather continues and we have an early spring then the virus may not have a chance to get a foothold,” Dr. Gerald Evans, a Queen’s University professor and chief of infectious diseases at Kingston General Hospital, said.
We just recovered from an intense season: Last year, emergency departments and hospitals braced for patients sick with H3N2, which is traditionally more potent. This year, H3N2 is one of the strains making its rounds again.
“It’s hard to ignore the fact that we had such massive activity last year. You have to recognize there will be some impact on population immunity – it may be an infection-induced immunity that’s longer lasting and broader and that’s keeping this particular epidemic strain at bay,” said Dr. Danuta Skowronski, a University of British Columbia professor. She also leads the B.C. Centre for Disease Control’s department of influenza and emerging respiratory pathogens.
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“We had such a bad H3N2 season last year, it may be a fairer percentage of people have antibodies against that strain now,” Gardam explained.
H1N1 – the pandemic strain that brought the country to its knees in 2009 – is also circulating in smaller numbers. It’s been included in the flu vaccine since that notorious year.
“We have lots of people who have been immunized so they’re protected against that strain. That may be an important factor in why we’re not getting a big bump in cases,” Gardam says.
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The vaccine is a match: Last year’s vaccine was only 23 per cent effective, according to health officials. It was among one of the worst efficacy rates recorded since the Centers for Disease Control and Prevention started tracking how well the vaccines work.
Typically, the best flu vaccines are 50 to 60 per cent effective. So far, this year’s vaccine appears to be a good fit.
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Each year, strains of the influenzas mutate and re-emerge, infecting victims and triggering a new season. Those of us in the Northern Hemisphere keep a watchful eye over the flu in the Southern Hemisphere, which affects residents during their winter (or our summer).
The flu season hit the Southern Hemisphere with little fanfare, hinting at a pretty tame season here, too.
“It’s primarily because the vaccine was a good match so we shouldn’t see a record year like last year,” Tetro says.
There’s still time: The flu virus typically makes an appearance by November, and by the end of January or the start of February, an upswing of illness hits the country and lingers for about four weeks before influenza dies down, Evans said.
Last year, peaking around Christmastime was an anomaly. The experts say if the temperatures stay cool, the flu could touch down in Canada in full force.
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“Those years when we saw it pick up in late December, my personal view is that that was early. We may be returning to our typical pattern where we see it peak at the end of winter,” Evans explained.
Gardam says there are typically two peaks – one in December as kids return home from school, germs in tow, and again in February, as frigid temperatures set in.
Flu viruses also tend to “drift” or mutate, so it may not be the same influenza we’re anticipating, Danuta warned.
“We don’t want to relax altogether. We’re constantly monitoring viruses but the good news, at this point, is this season is much milder,” she said.
carmen.chai@globalnews.ca
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