From 2018-01-09

Canada's chief public health officer says it's possible that this year's flu vaccine may have limited effectiveness against a particularly severe strain of influenza A that appears to be dominant throughout Canada.  

"In Canada it's still too early to actually tell how effective this vaccine will be," Dr. Theresa Tam told CBC News. "There is a potential ... of low vaccine effectiveness, but we really can't tell at this point in time."  

The reason for believing there's a potential weakness in the vaccine, Tam said, is the fact that countries in the Southern Hemisphere, which have their flu season before Northern Hemisphere countries, experienced "poor vaccine effectiveness" against H3N2, a subtype of influenza A that tends to cause more severe illness among vulnerable people, including the elderly and children. 

In addition, studies suggest that the process of manufacturing the vaccine may have compromised its effectiveness against H3N2 because it can mutate when grown in eggs — and Canada uses egg-based vaccines, Tam said.  

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