Toronto, ON — Health officials report that the H1N1 influenza strain remains the dominant subtype circulating in Canada, though H3N2 cases are rising, raising concerns about the severity of the upcoming flu season. Infectious disease specialists say that while it’s unclear which strain will ultimately dominate, getting the flu shot remains the best protection against infection, hospitalization, and complications.
According to Health Canada’s respiratory virus surveillance report released on November 7, H1N1 was the leading subtype for the week ending November 1. During that week, 431 flu cases were detected from 22,421 tests, representing a 1.9 per cent positivity rate. The highest number of influenza detections occurred among adults aged 65 and older, with a hospitalization rate of 0.1 per 100,000 population.
However, health experts are closely watching the H3N2 strain, another subtype of influenza A that has begun to circulate more widely in Northern Hemisphere countries, including Canada. Dr. Isaac Bogoch, infectious disease specialist at Toronto General Hospital, said that while it’s too early to tell which strain will prevail, H3N2 seasons are often more severe.
“In a typical flu season, one of these subtypes — H1N1 or H3N2 — becomes dominant,” Dr. Bogoch told CityNews. “It’s not quite clear if H3N2 will overtake H1N1 this year, but when it does, those seasons tend to be more severe.”
This year’s flu vaccine has been formulated to protect against both H1N1 and H3N2, as well as an influenza B strain. While some early data suggests the H3N2 strain could show mild variation from the vaccine, infectious disease experts emphasize that vaccination remains crucial.
“Regardless of how well the vaccine matches, getting the flu shot still helps,” said Dr. Dale Kalina Samji, infectious disease specialist. “There’s always some degree of cross-protection that reduces your risk of infection and severe illness.”
Dr. Zainab Abdurrahman, President of the Ontario Medical Association, called this year’s flu season a potential “wake-up call,” referencing Australia’s record-breaking 2025 outbreak that saw more than 410,000 lab-confirmed flu cases, up from 365,000 the year before. “We don’t want to see those same numbers here,” she said. “Vaccination is the key to prevention.”
As of October 27, Ontario residents can receive free flu and COVID-19 vaccines at pharmacies, public health units, and family doctors’ offices. The Ontario Ministry of Health is urging all residents, especially seniors, young children, and those with underlying health conditions, to get vaccinated as early as possible.
Dr. Abdurrahman, who is also a clinical immunologist, addressed concerns about vaccine allergies and side effects. “We understand some people may have questions or hesitations,” she said. “Mild reactions like arm soreness or fatigue are normal. For rare allergic cases, allergists can safely revaccinate patients using incremental dosing methods.”
She added that vaccines are rigorously tested and proven safe. “The science is clear — vaccines save lives. It’s completely fine to have questions, but it’s important to talk them through with a trusted healthcare provider.”
As influenza activity continues to climb, experts say the message is simple: get vaccinated, stay home if sick, and practice good hygiene to reduce the spread of respiratory viruses this winter.