A group of infectious disease experts estimates that this season's influenza vaccine has been more than 40 per cent effective in preventing the respiratory illness in Canadians who got the shot.

The Canadian Sentinel Practitioner Surveillance Network determines vaccine effectiveness by analyzing how many inoculated people tested positive for the flu virus compared to those who were unvaccinated.

Lead researcher Dr. Danuta Skowronski of the B.C. Centre for Disease Control says the 42 per cent effectiveness rating isn't as high as physicians would like, but the level of protection against the flu is still "decent."

That effectiveness level means the risk of getting sick enough to require medical attention is almost cut in half. And Skowronski says that's important for the elderly and those with underlying health conditions at risk for hospitalization and even death from the flu.

She says the vaccine has been much better at preventing cases of the H3N2 influenza strain circulating this season compared to 2014-15 shot, which was a mismatch for that year's genetic variation of the H3N2 strain.

Skowronski says H3N2 has been responsible for 95 per cent of flu cases this season, but the number of new cases occurring in Canada has now begun to wane.