Toronto, ON — Ontario may be heading into one of its most challenging flu seasons in recent years, according to Public Health Ontario (PHO) and medical experts who are warning of a significant rise in influenza activity across the province and the country.
PHO’s latest surveillance data shows a 1.8 per cent increase in flu cases during the final week of October, with three outbreaks, 14 hospitalizations, and 129 confirmed cases reported. The agency predicts flu activity will continue to rise through mid-November, particularly among children and adolescents.
Across Canada, federal health data indicates that nearly two per cent of national flu tests have returned positive — still below the five per cent threshold that marks an epidemic but reflecting a noticeable upward trend compared to previous weeks.
Health officials are watching developments in the southern hemisphere, where countries such as Australia experienced one of their worst flu seasons on record earlier this year. “What we’re seeing in Australia — a very, very bad year — often foreshadows what’s coming for us,” said Dr. Fahad Razak, internal medicine specialist at St. Michael’s Hospital.
In Australia, the Royal Australian College of General Practitioners reported flu infections reaching record levels this October, with about 1.5 per cent of the population contracting a notifiable flu infection — an 11 per cent increase over 2024. Alarmingly, vaccination rates among young children dropped to the lowest level since 2021, with only one in four receiving a flu shot.
Canada’s own Public Health Agency (PHAC) cautions that trends from the southern hemisphere do not always directly translate to Canada’s experience, given differences in circulating strains and climate. However, one strain drawing concern is H3N2, a subtype of influenza A known to cause more severe illness in infants, seniors, and immunocompromised individuals.
“H3N2 has that capacity to cause worse flu seasons,” said Dr. Alon Vaisman, infectious disease physician at University Health Network. “It’s been less common in recent years, which means many people’s immune systems — and vaccines — haven’t encountered it recently.”
For the past 15 years, H1N1 has been the dominant influenza strain in Canada. But this year, national data shows a 50/50 split between H1N1 and H3N2, raising concerns that a shift in dominant strains could reduce vaccine effectiveness.
“What’s a little bit concerning is that some H3N2 samples show mild resistance to the current vaccine,” said Dr. Isaac Bogoch, infectious disease specialist at Toronto General Hospital. “That doesn’t mean the vaccine won’t work — but it may be somewhat less effective against this particular strain.”
This year’s flu shot targets two influenza A subtypes (H1N1 and H3N2) and one influenza B strain. Despite potential variation in protection, experts strongly urge Ontarians to get vaccinated, emphasizing that it remains the most effective way to reduce serious illness, hospitalization, and community transmission.
“Even if the vaccine isn’t a perfect match, it still provides substantial protection,” Bogoch said. “It’s far better to get the shot than to go without.”
Other public health measures remain equally important, doctors say: staying home when sick, washing hands regularly, and avoiding close contact in crowded spaces. “The fundamentals don’t change,” Dr. Vaisman added. “The best way to prevent the flu is still the same — vaccination, hygiene, and staying home if you’re unwell.”
While it’s still too early to predict the exact severity of this year’s flu season, experts expect the peak to arrive in late December or early January. The coming weeks, they warn, will determine whether Ontario faces a moderate wave — or a very tough one.