With flu infections starting to climb across Canada, doctors and public health specialists are preparing for a challenging influenza season. The concern centres on the global spread of a changing H3N2 strain that may not line up well with this year’s flu vaccine. Fresh federal figures released on Friday show that about two per cent of flu tests nationwide returned positive results last week. While that remains below the five per cent threshold Canada uses to officially declare a seasonal flu outbreak, it marks a clear rise compared to recent weeks.Outside Canada, the current flu season has already been severe, with record case numbers reported in the Southern Hemisphere and an earlier-than-usual surge seen in parts of Asia and the United Kingdom. As winter approaches, experts say these trends could offer clues about what Canada might face. “This is the second year in a row that the Southern Hemisphere has seen higher-than-average influenza activity,” said Dr. Jesse Papenburg, a pediatric infectious disease expert at Montreal Children’s Hospital and the McGill University Health Centre, as per CTV News.“When you look at case numbers, last year was likely the worst flu season Canada experienced in about ten years. Based on what we’re seeing so far, there’s a real possibility we could see a similar level of severity again,” he added.Influenza A: What Is Leading To The Surge?Some specialists believe a changing version of H3N2 is driving the early rise in cases. This form of influenza A is already known for causing more serious illness, particularly in older adults. What is raising extra concern this year is that recent mutations appear to be creating more distance between the circulating virus and the protection offered by the current flu shot. Dr. Danuta Skowronski, who leads influenza and emerging respiratory pathogen epidemiology at the B.C. Centre for Disease Control, is one of several Canadian experts closely tracking these changes, according to CTV News.Influenza A: Experts Warn Of Vaccine MismatchAlthough the H3N2 subtype had remained relatively stable for years, Skowronski says it has recently begun showing sharper structural shifts as it spread into northern regions. These changes suggest the strain now circulating could be poorly matched to this season’s vaccine. The current flu shot is designed to protect against two influenza A strains, including H1N1 and H3N2, along with one influenza B strain. “There’s actually a fairly large gap between the H3N2 virus we’re seeing circulate and the one included in the vaccine,” Skowronski explained. “That’s not due to any error. It reflects how unpredictable and fast-changing influenza viruses can be.”In a statement shared with CBC News, the Public Health Agency of Canada said it keeps close watch on respiratory virus trends around the world to identify patterns that could affect Canadians.The agency also noted that flu data from the Southern Hemisphere does not always directly forecast what will happen in Canada, since seasonal patterns and population dynamics can differ.“At this point, it’s still too early to say how severe Canada’s flu season will be,” the agency said, adding that factors such as which influenza subtype becomes dominant, the presence of other respiratory viruses, vaccine performance, and vaccination rates will all play a role.Even if this year’s vaccine turns out to be less closely matched to the evolving H3N2 strain, all three experts emphasized that getting the flu shot remains important, especially for older adults across Canada.