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Flu shot offers modest protection this year in U.S.; Canadian numbers likely lower

A new report from American scientists suggests this year’s flu vaccine is offering modest levels of protection against the influenza viruses that are in circulation.

And while Canadian estimates are still being worked on, there is reason to suspect the vaccine effectiveness in this country may be lower still than what is being seen south of the border.

The report, published today by the U.S. Centers for Disease Control, suggests on average the vaccine lowers a person’s risk of getting sick enough to need medical care by 23 per cent.

That low level of protection is attributed to the fact that the H3N2 viruses that are causing most of the flu this year in North America aren’t a good match for the one in this year’s vaccine.

The CDC report says about two-thirds of the H3N2 viruses seen in the U.S. so far this winter are not the type included in the vaccine because the viruses have mutated or drifted.

A leading Canadian flu researcher says in Canada, nearly all the H3N2 viruses that are being seen are drifted viruses, so the vaccine may be working less well here.

Dr. Danuta Skowronski of the British Columbia Centre for Disease Control says the U.S. study shows modest protection in children aged six months to 17 years.

But in 18- to 49-year-olds, and people aged 50 or older, the protection is 12 and 14 per cent respectively — and the numbers aren’t statistically significant. That means the protection offered in these groups could be higher — but could be lower as well.

“I would qualify these findings as showing little or no protection. And I don’t think we should expect the Canadian estimates to be higher, given that we have a greater proportion of drift variants (viruses),” Skowronski says.

She and colleagues across the country are currently working to generate vaccine effectiveness estimates for Canada for this season.