People who got the flu shot had no protection against the dominant strain of influenza circulating this winter, public health officials now say.

The H3N2 virus was once again prevalent this year and the vaccine has performed poorly against it in recent years because of a mismatch, with about 40 per cent effectiveness in 2010-11 and 2012-13 compared to upwards of 70 per cent when there’s a good match.

But this year’s protection turned out to be “as close to zero as you can get,” according to B.C. Centre for Disease Control epidemiologist Dr. Danuta Skowronski.

“It is frankly the lowest vaccine effectiveness that we have measured through our network in the past decade,” she said. “It’s stupendously bad.”

Skowronski said the results her office has compiled from B.C., Alberta, Ontario and Quebec are similar to findings in the U.S.

She said it’s becoming clear the underperforming H3N2 component of the vaccine needs to be replaced with a better match to the strain in circulation.

This year’s dismal performance of the vaccine has Skowronski cautioning people at high risk that they’re “not invincible” if they were vaccinated and should seek early antiviral treatment at the first sign of flu symptoms, while also avoiding ill people.

Flu vaccine also contains components to counter the H1N1 and influenza B strains, so it’s still effective against them in years when those virus types are more prevalent.

Also troubling is an emerging pattern from multiple studies, including the BCCDC data, that suggests flu vaccinations are less effective if the person also had the flu shot the previous year.

Asked if that suggests people would be better off to get vaccinated only every second year, Skowronski said it’s too early and “potentially dangerous” to make major changes to recommendations right now.

Nor would she comment on the effectiveness of B.C.’s policy of requiring unvaccinated nurses to wear a mask when treating patients in light of the latest research.

“Currently there’s almost a sense it’s anti-Canadian if you don’t get this vaccine,” Skowronski said. “Our results offer a more sober, thoughtful perspective on what can be achieved, what can be the program benefits. It suggests we need to take a more strategic look at that.”

The new findings come as public health officials continue to struggle to persuade enough parents to vaccinate their children against other preventable diseases to ensure adequate levels of immunity.

The problems with the flu vaccine don’t diminish the value of other “excellent” vaccination programs, Skowronski said, but added public disclosure of underperformance is important.

“There are issues with this flu vaccine,” Skowronski said. “We need to be up front about that for the sake of our collective credibility.”