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A staff worker receives a flu vaccination at the Victoria General Hospital in Victoria, B.C.,Tuesday October 21, 2014.CHAD HIPOLITO/The Globe and Mail

A Canadian study has confirmed what many doctors have suspected for weeks: This year's flu vaccine doesn't seem to protect against the H3N2 virus, the dominant strain in circulation.

B.C. researchers studied data from patients in that province, as well as Alberta, Ontario and Quebec, and found that a high number of laboratory-confirmed influenza cases occurred in people who had been vaccinated.

The researchers have concluded the vaccine offers very little benefit, with one notable exception: People who did not get a flu shot last year but did get one this year seemed to have some protection against H3N2, though it is unclear why.

Although flu shot's efficacy varies each year, this season's dismal results are prompting many Canadians to question why we even need an influenza-immunization program.

Here is a primer on what you need to know about the flu shot – this year and beyond:

Why is this year's flu shot unable to offer much protection?

That's not entirely clear, but it's likely due to a combination of factors, including mutations in the circulating virus, says Danuta Skowronski, epidemiology lead for influenza and emerging respiratory pathogens at the BC Centre for Disease Control, and author of the study on flu shot effectiveness.

Dr. Skowronski adds that it's always a tough year when H3N2 is the dominant strain. Hospitalizations and deaths go up and the vaccine's effectiveness is usually low (although she can't recall another year when the effectiveness rates were this low).

Does this mean the flu shot doesn't work?

This year, for the most part, yes. The vaccine doesn't seem to be able to thwart the H3N2 virus, which is causing the vast majority of flu cases.

Experts are urging those most vulnerable to the flu, such as the elderly or those with underlying conditions, to take extra precautions, such as avoiding anyone who may have the flu or seeking medical attention early if they believe they have caught the virus.

Last year, however, the flu vaccine was more than 60-per-cent effective. Previous studies also suggest that most years the flu shot is around 60-per-cent effective in healthy adults, although that number may be lower in children and those over the age of 65.

So why bother having an expensive flu shot program if it only works 60 per cent of the time, even in good years?

Only in the past decade have researchers been able to accurately track how well the flu shot works. Dr. Skowronski and her team developed a system, now employed around the world, that uses data from a group of doctors who track flu cases.

This new model is allowing researchers to develop, for the first time, a much deeper understanding of the true benefits and limits of the current flu vaccine. And from what she's seeing, Dr. Skowronski believes it's time to change the current approach to the vaccine, considering how expensive it is to administer, how often it must be given and how limited the benefits may be for some age groups.

"We really have expanded influenza immunization," she said.

"It's time for a strategic look at that." The flu shot is still a valuable tool in the fight against influenza, she said, but current messages that urge everyone to get immunized each year may have to be revised, based on what we know about how likely it is the flu shot will work.

Is there ever going to be a way to prevent the flu 100 per cent of the time?

A universal flu vaccine is known as the "holy grail" among influenza researchers.

Think of the flu virus as a lollipop, they say: Each year, the head of the lollipop changes, depending on what virus is in circulation, and that is what the vaccine targets. But the stem remains the same. It's believed that developing a vaccine that can properly target the stem may be the key to a universal vaccine.

But there are still so many unknowns and it's difficult to predict when, or if, this vaccine will be a reality. Dr. Skowronski said it will be impossible to do unless governments make it a priority and provide the necessary funding.

"We didn't put a man on the moon because we said, well, maybe someone, somewhere, some day will figure out how to do it," Dr. Skowronski said.

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