Photo: Flickr/Creative Commons, Michael.

By all accounts, the 2017-2018 flu season was a nasty one. The CBC reported that, by January 2018, there were 20 times more detections of influenza B than for the same period in the preceding seven years. Even worse, some reports pegged the efficacy of the 2017-2018 flu vaccine at just 10 to 20 percent.

Dr. Michelle Murti of Public Health Ontario reports that the last flu season was, indeed, unusual. “During a typical flu season, we might see influenza A activity peak in January and then begin to recede, just in time for influenza B to make its appearance,” she says.

“There was a lot of flu going around and your chances of getting flu was higher for a longer period.”

Human influenza strains are classified into A and B, depending on their ability to cause a pandemic. But last year, both strains peaked early and stuck around, making for particularly high influenza activity. “There was a lot of flu going around and your chances of getting flu was higher for a longer period.”

Early summer might seem like a funny time to be talking about flu season, but the planning for the vaccine actually starts well before mittens and sniffles season. Public health officials conduct regular testing to gauge which strains are attacking and where, and the decisions about what goes into the following year’s flu vaccine are made by the World Health Organization (WHO) in February. It’s essential to complete this process early enough that sufficient batches can be made and distributed internationally in time for the next flu season.

Flu shots are recommended for older adults, caregivers and people with underlying health conditions. Photo: Flickr/Creative Commons, Steve Beshear.

The WHO actually releases separate vaccination products for the southern and northern hemispheres, based on their respective winters, and scientists look at what’s happening in the present season (and what happened in the other hemisphere’s recent season) to inform the vaccine for the next. The influenza vaccine typically contains two types of influenza A and one type of influenza B, though some vaccines include an additional type of influenza A (for a total of four strains of the virus).

“They look at the information and make a determination about what’s more likely to be circulating in the coming season,” says Murti. “And it is a prediction so we’re not always sure but it is based on what we know at the time.” The Public Health Agency of Canada has a weekly FluWatch report, which confirms the type and number of laboratory-confirmed flu cases – a number that tends to be much lower than the absolute number of flu cases because most people don’t seek medical attention for the flu.

The main change for the northern hemisphere vaccine for the 2018-2019 season is the inclusion of H3N2, the nasty influenza A strain that proved to be the dominant circulating strain in the 2017-2018 flu season – though the exact ratio of H3N3 to other strains varied from region to region.

But despite the careful calibrations that go into formulating the influenza vaccine, a new report from the National Institute on Aging at Ryerson University found that less than a third of all Canadians and less than two-thirds of older Canadians receive the vaccine every year. (Health Canada recommends an 80 percent vaccination rate.) According to the same report, influenza is the seventh leading cause of death in Canada.

“We’re always trying to do better, especially for people who are at particularly high risk, including seniors, people with underlying health conditions, children under five, and workers who come into contact with people who are high risk,” says Murti.

Canadian public health officials recommend getting your flu shot when it becomes available in October, as it takes the vaccine a few weeks to be fully activated in the body, ensuring you’re protected for a flu season that typically starts in November.