Why the H3N2 flu is hitting Canada hard this year

Canada is being hit hard by the flu bug, whose dominant strain this year, the influenza A H3N2 flu virus subtype, continues to make people sick despite the medical community’s best efforts at protecting against it.

Hospitals and emergency rooms across the country are filling up with people struggling to deal with flu infections, and officials are saying that the outbreak is expected to get a lot worse before it gets better, thanks to a nasty strain of the H3N2 virus that’s managed to avoid getting pinned down by this year’s flu immunization program.

In Alberta, the latest news has 1,700 confirmed cases of the flu in the province, many of them coming from Calgary where well over 1,000 cases have been confirmed. So far, reports are saying that 13 people have died from complications from the illness and five of those were in Calgary. “It’s a more difficult one,” says Calgary’s medical officer of health, Dr. Judy MacDonald, speaking to the CBC about this year’s strain of H3N2. “It typically causes a little more severe illness, especially in the extremes of age.”

Last week, a reported 340 people were admitted to hospitals in Hamilton, where officials are asking the public to help in limiting the spread of the virus, especially by staying home if you have the flu and postponing visits to hospitals to see loved ones until you’re feeling better. “Some people – including infants and the elderly – are at a higher risk of developing complications from the flu,” says Dr. Jeff Pernica, infectious disease physician at Hamilton Health Sciences. “So, it’s up to each of us to do our part to fight the flu, not just for our own health, but for the health of those around us.”

The H3N2 influenza virus has been on the health radar for some time now as a particularly difficult influenza virus subtype. In 1968, H3N2 emerged as a category 2 pandemic known as the Hong Kong Flu, responsible for one million deaths worldwide and infecting over half a million residents of Hong Kong alone. Since then, H3N2 has kept up regular appearances worldwide, often confounding best efforts to immunize citizens against it.

Each year, the dominant virus subtypes change, prompting officials to issue flu vaccines which they expect will match the upcoming year’s most prevalent forms. This year’s flu vaccine in Canada was, in fact, meant to protect against both the H1N1 and H3N2 subtypes of influenza A, but because of H3N2’s quick ability to mutate, the match between vaccine and this year’s version of the virus is not exact, thus leading to the current outbreaks.

And as in the 2014-15 season, where the flu vaccine proved to be only 10 per cent effective against that year’s strain of H3N2, officials are now concerned about how well the current vaccine will do against H3N2. Daunta Skowronski, epidemiology lead for influenza and emerging respiratory pathogens at the B.C. Centre for Disease Control, says that she’d be happy with a 40 to 50 per cent protection rate.

“We’re still spiking,” said Skowronski in conversation with the Globe and Mail. “I can’t say that we have peaked.”

Skowronski urges that even though the numbers aren’t particularly high, the flu vaccine still offers the best protection against contracting the flu. “If you’re a person at higher risk of hospitalization or death, cutting your risk in half or even by a third is really important protection,” she said.