As flu cases begin rising again across Canada, scientists are paying close attention to an emerging form of the H3N2 strain that may not be an ideal match for this year’s seasonal vaccine. Despite that potential mismatch, medical experts say Canadians should still get the flu shot — stressing it remains one of the most effective tools for preventing severe illness, hospitalization, and death.
Influenza is already gaining momentum, following a tough season in the southern hemisphere, and researchers are monitoring mutations in H3N2 that could reduce how well this year’s vaccine prevents infection. H3N2 is known for causing more serious disease and appears to be evolving in a way that puts it out of sync with the current formulation.
But the question many are now asking — is there any point in getting the shot? — has a clear answer from scientists: absolutely.
Flu vaccine effectiveness changes from year to year because the virus mutates constantly. That means the ability of the vaccine to prevent infection outright can vary, but its protection against severe disease remains strong. “Most people aren’t worried about getting a cough or a sniffle. What matters is staying out of the hospital,” said Matthew Miller, an immunologist and researcher at McMaster University. His recent analysis of hundreds of studies found that flu shots consistently reduce the severity of illness, even when not perfectly matched to circulating strains.
Vaccination also helps reduce transmission, protecting vulnerable groups such as older adults, infants, and people with chronic health conditions. Dr. Brian Conway, an infectious disease specialist in Vancouver, noted that roughly 90 per cent of Canadians who died from influenza or pneumonia in 2022 were aged 65 and older. “You should run, not walk, and get the flu shot right now,” he said.
Canada’s National Advisory Committee on Immunization strongly recommends annual flu shots for everyone six months and older, with particular emphasis on older adults, young children, pregnant people, and those with underlying health issues. Even healthy young adults can become seriously ill; U.S. data from last season showed more than one in 10 flu-related hospitalizations occurred in people with no pre-existing conditions.
Skipping the flu shot significantly increases the risk of serious outcomes. Last season, two-thirds of hospitalized flu patients in the U.S. were unvaccinated, and 90 per cent of children who died from influenza had not been fully vaccinated.
This year’s vaccine includes protection against several influenza A and B strains, including H1N1 and older H3N2 variants. A CDC study found that in the southern hemisphere, the same vaccine formulation cut flu-related hospitalizations by about half. But with H3N2 now mutating, experts acknowledge that protection against infection may be weaker in Canada.
Even so, researchers emphasize that the flu shot can still blunt the impact of the virus. Dr. Danuta Skowronski of the B.C. Centre for Disease Control said the vaccine guards against multiple flu strains — not just the version of H3N2 that is evolving — and provides broad immune protection that reduces severe outcomes.
Miller agreed that the potential mismatch only reinforces the importance of getting vaccinated. “Even though it might not be a great match, its ability to prevent severe infection further highlights why people should get it,” he said, noting that keeping patients out of Canada’s strained hospital system is essential as respiratory virus season ramps up.
Experts say the takeaway is simple: a mismatched vaccine is still far better than no protection at all.