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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.
The potential for lower vaccine effectiveness makes it even more important that Canadians take “other measures” to protect themselves against the flu, she said, including handwashing, coughing into your sleeve, disposing of used tissues, and staying home when you’re sick.
“Given the mix of influenza viruses circulating right now and more could still circulate later on in the ensuing months, we still recommend influenza vaccine for Canadians over six months of age,” she said.
Although children are more susceptible to serious illness from H3N2 than the general population, they are also particularly vulnerable to the “B” strain, possibly because of their lack of previous exposure, she said.
Tam said that given the burden of influenza B on kids, the national advisory committee on immunization recommends children receive the “quadrivalent” vaccine, which protects against four strains of flu, including two B strains. The quadrivalent vaccine available in Canada right now covers the B strain that is currently circulating, she said. The other type of vaccine — called “trivalent” because it covers three strains of flu — “unfortunately” doesn’t cover that B strain.
Parents can ask their local public health agencies which vaccine is available in their area, she said.
“Influenza is in full swing in Canada,” said Tam, noting that this year’s flu season started earlier than normal.
PHAC’s flu surveillance data are consistent with what health-care providers are observing, said Dr. Isaac Bogoch, an infectious disease specialist at University Health Network in Toronto.
“There are early indicators that this influenza season is a little bit more severe compared to prior influenza seasons. Certainly we’re seeing that in the hospital,” he said.
“We know that the years when there areH3N2 strains that predominate, those are more severe years — meaning there are typically more infections, more severe infections, more hospitalizations and more deaths.”
Despite that, he said, “it’s still extremely important to get the vaccine.”
“Anyone that’s had influenza, and I mean real influenza — not a sniffle or a cough or a cold — but real, true influenza, they’ll know how severe this can be,” Bogoch said. “I think many people would readily take that 10-per-cent reduction in risk just because this can be such a debilitating and severe illness.”
“Even though it’s not perfect, it’s still the best protection we have.”