Flu shot's 'crystal ball' science still best bet against influenza

The seasonal flu shot is designed by the world's top scientists who have access to a global network of influenza data — but at the end of the day, it's still just guesswork.

Most of the time, they get it right. Other times, like last year in Canada, they miss the mark completely.

Still, medical experts say it is our best defence against a virus that kills thousands of Canadians every year.

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"People will be a bit cavalier about the flu, but in fact, it is a significant illness for people and even fatal for some," Joshua Tepper, a family physician and CEO of Health Quality Ontario, told CBC News. 

An estimated 12,500 people are admitted to hospital each year for complications arising from the flu and about 3,500 die, according to the Public Health Agency of Canada.

"The flu vaccine remains the first line of defence," Tepper said. "Even when it's not a perfect match, it still offers protection, and there's very little downside."

How the flu shot gets made

Every February, based on the flu virus strains circulating at the time, the World Health Organization chooses which ones should be included in the seasonal vaccines that will be distributed in the northern hemisphere the following autumn. (A similar process happens later in the year to decide on the flu vaccine for the southern hemisphere's fall season).

"They're looking in the crystal ball and gazing ahead," said Meena Dawar, medical officer of health at Vancouver Coastal Health. "And they have pretty good experience at estimating vaccination candidates most of the time, given that they have decades of experience doing this."

The decisions are based on enormous amount of data that's collected on influenza year-round from 140 test centres in 100 countries, all of which is sent to five WHO centres for analysis, Tepper said. 

"We're constantly monitoring the virus around the world," he said. 

There are three types of influenza virus — A, B and C. Human influenza A and B are the types that cause seasonal epidemics in North America almost every winter, according to the U.S. Centers for Disease Control.

The  seasonal flu shot is trivalent, which means it's configured to protect against against two A strains, H3N2 and H1N1, and one of two B-lineage influenza viruses. 

Once the year's formula has been decided, it takes manufacturers six months to produce the vaccine and stockpile enough doses to supply Canada 's provinces and territories for their inoculation programs, which usually take place in mid- to late-October. 

Last year's flop

Despite the reams of data and experts' best efforts, there's always a risk the flu shot won't work. Vaccine production takes time and viruses mutate.

Last year's flu shot was a bust in Canada because by the time people got immunized, the dominant H3N2 bug affecting the population had changed so dramatically it was no longer genetically similar to the H3N2 component in the vaccine.

Dawar called last year's failure "highly unusual." Rarely does the flu shot provide an exact match for the dominant circulating strain, but it's usually close enough to make a difference. 

"I've been working the public health field for a decade now and I haven't seen it happen before," Dawar said. "Most of the time, they get it bang on."

This season's trivalent shot contains the evolved H3N2 strain from last year, as well as H1N1 and B/Phuket.

Making progress

Each year, scientists take into account the previous year's successes and failures — but are they getting any better at making an effective flu shot?

"People are constantly seeking to improve the process and streamline it," Tepper said. "The challenge is you have to provide millions of doses of the vaccine, and that takes time. The reality is the production and distribution takes time."

Still, health officials are making progress, especially when it comes to protecting those most vulnerable to influenza — children and the elderly.

For the first time this year, Ontario's public health insurance will covering a nasal spray version of the flu vaccine for children. 

"It's less invasive. We want to see uptake in all populations increase, but especially in our vulnerable groups, which include children," Justeen Mansourian-Christakos, a nurse with the Sudbury and District Health Unit, told CBC News. 

Most other provinces started offering the spray in recent years. New Brunswick and Nova Scotia are the only remaining provinces that don't cover it. 

For the first time this year, Canada has approved the use of a four-strain, or quadrivalent, vaccine that contains a second B-lineage virus called B/Brisbane.

Alberta, B.C., Ontario and P.E.I. are offering it exclusively to children, who are more susceptible to B strains. Quebec is giving it to infants and children with low immune function. The other provinces and territories are making it available both to children and adults. 

In the future, we may also see a specific vaccine tailored to the elderly, Tepper said.

A Canada-U.S. study published in the New England Journal of Medicine last year found a higher dose is more effective for people over 65.

"I think this is an emerging area we'll be hearing more about," Tepper said.

'The only way'

Shortcomings aside, health-care professionals across Canada continue to encourage everyone get their annual flu shot. 

"We absolutely recommend that Canadians get their vaccine," Dawar said. "It's very important to protect yourself from influenza, and getting the flu shot is the only way to project yourself from getting the flu."

What's more, she said, if getting vaccinated doesn't protect you from the flu outright, you'll still likely experience a milder form of it.

Tepper said people should take others into consideration when deciding whether to get vaccinated. 

"You're not always getting the vaccine to keep yourself healthy. You're getting the vaccine to keep those around you healthy, particularly those who are very young or very old."