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Flu Season | Comparing strains

H1N1 vs. H3N2: What flu strains make for a severe season


Michelle Mackey
Weather Broadcaster

Monday, January 14, 2019, 3:49 PM - H1N1 is back. The 2018-19 flu season has seen a resurgence in the strain of swine flu that killed over 400 Canadians during the 2009 pandemic. Does this mean that this season is more severe than years past?

For Dr. Isaac Bogoch, an infectious disease physician at Toronto General Hospital, the answer is no.

"It’s still too early to really judge if this is going to be a more severe season in comparison to other seasons," says Dr. Bogoch. "I would wager that this year’s influenza season will be a typical influenza season, and not be anything more severe than what we would have expected."

According to Dr. Bogoch, last season was worse as the H3N2 strain was predominate.

"At a population level, typically seasons that are H3N2, those are typically more severe seasons."

Bogoch says there are more hospitalizations and more deaths with H3N2, compared to seasons that are H1N1.

Image courtesy of Getty Images

"On top of that, the vaccinations for last year’s flu virus wasn’t as effective as we would have liked it to be," says Dr. Bogoch.

In the image below you can see that stateside, the highest incidence of flu has been in the central U.S.

Jason Persoff, MD, SFHM, Assistant Professor of Hospital Internal Medicine at the University of Colorado, believes this flu season will be markedly severe as we continue to move through it.

"A majority of my patients who have required the ICU or who have died have been in their 20s and 30s, which is usually a sign of a serious flu season ahead."

Source: CDC, Centers for Disease Control and Prevention

In Canada, the flu season started in late October, two weeks earlier than the 2017-18 season. However, the Public Health Agency of Canada (PHAC) says this is not out of the ordinary.

"The timing of the influenza season varies from year to year, and typically falls between October and May, so this early start was not unusual," says the agency in a statement. 

Regardless of the strain, influenza is a serious viral infection that can cause fever, body aches, fatigue, nausea and diarrhea. It can also be deadly.

"…It’s so serious that it kills over half a million people per year on Earth," says Dr Bogoch. 

Six pediatric deaths have occurred so far this season in Canada -- all children under the age of 10. There were also 95 pediatric admissions to ICU for flu.

Flu season peaks mid to late January and begins to decline into February. However, it is not too late to get the flu shot. The PHAC says this is the most effective way to reduce your risk of getting the flu. 

The populations most at risk of developing severe complications from influenza are people with chronic disease, those who are 65 years of age and over, children over six months, and pregnant women. For those unable to get the flu shot, such as babies under six months of age, the PHAC suggests those around the infants get vaccinated to help provide protection from the flu.

According to the Centers for Disease Control and Prevention, recent studies show that flu vaccination reduces the risk of flu illness by between 40 and 60 per cent among the overall population during seasons when most circulating flu viruses are well-matched to the flu vaccine.

However, Dr. Persoff states that even partial efficacy of the flu shot saves lives.

"Not one of my patients who has been hospitalized with flu, but who had the vaccine has required ICU level care or has died."

Along with the flu shot, you can protect yourself and others by not touching your face, washing your hands often, coughing/sneezing into your arm instead of your hand, and cleaning frequent contact surfaces. And if you do get sick, stay home.

RELATED: H1N1 is back: What you need to know about this latest flu season


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