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Canada is experiencing a significant surge in influenza cases, with the national test positivity rate reaching 24.3% in the first week of February, according to data from the Canadian Respiratory Virus Surveillance Report.
In the week ending February 8, there were 10,449 confirmed cases of influenza. The majority (94%) were caused by influenza A (H1N1), while 6% resulted from influenza B (H3N2). The highest number of detections were among individuals aged 65 and older, and the hospitalization rate has climbed to 3.4 per 100,000 people. Quebec is currently the most affected province.
Dr. Jesse Papenburg, an associate professor of pediatrics at McGill University and pediatrician at Montreal Children’s Hospital, noted a sharp increase in influenza-like illnesses in children.
“In Canada, we prioritize therapy for high-risk outpatients or those requiring hospitalization,” Dr. Papenburg said. “Most healthy children with influenza don’t need antiviral treatment. However, we’re seeing a steady rise in hospitalizations, and some children even require intensive care.”
Impact of the COVID-19 Pandemic on Influenza Trends
Dr. Christopher Labos, a lecturer at McGill University, explained that the prevalence of influenza was relatively low during the early years of the COVID-19 pandemic due to mask-wearing, social distancing, and reduced gatherings.
“Compared to those years, flu cases seem higher now,” said Dr. Labos. “We only get a clear picture of how severe a flu season is in retrospect, but this year appears to be particularly bad.”
Concerns Over Dual Influenza A Strains
Experts note that this year’s flu season is notable due to the concurrent circulation of both H1N1 and H3N2 strains.
“It’s almost like we are dealing with two outbreaks simultaneously,” said Dr. Papenburg. “Historically, H3N2 has disproportionately affected older adults, while past seasons with predominant H1N1 activity have had different demographic impacts.”
During the 2014-2015 flu season, for instance, H3N2 caused a high number of adult hospitalizations and influenza-related deaths, particularly because the vaccine did not match the circulating strain. Conversely, the 2022-2023 season saw an early and intense impact on children, despite an acceptable vaccine match.
Vaccine Effectiveness and Emerging Variants
Early estimates indicate that the current flu vaccine is approximately 50% effective against both H1N1 and H3N2 strains.
“The vaccine is performing decently well,” said Dr. Danuta M. Skowronski, an epidemiology expert at the BC Centre for Disease Control. “It cuts the risk of severe influenza by about half, which is significant protection.”
However, researchers have identified concerning new variants of both H1N1 and H3N2, raising questions about the effectiveness of next season’s vaccine. The World Health Organization (WHO) is set to decide on vaccine component changes by the end of February.
Preventive Measures and Public Health Recommendations
Health experts emphasize the importance of flu vaccination as the most effective way to prevent severe illness.
“Vaccination makes the biggest difference in determining whether someone gets sick or seriously ill,” Dr. Labos said. “Other preventive measures include staying home when sick, wearing a mask in public if symptomatic, and maintaining distance from others.”
Dr. Labos also highlighted the role of indoor air quality in virus transmission. “Using air filtration systems in office buildings and schools can help reduce the spread of respiratory viruses,” he said.
Financial Disclosures
Dr. Papenburg reported receiving grants from Merck and consulting fees from Enanta. Dr. Labos and Dr. Skowronski disclosed no relevant financial relationships.
Disclaimer: This article is based on publicly available data and expert opinions as of February 2025. It is intended for informational purposes only and should not be considered medical advice. Readers are encouraged to consult healthcare professionals for personalized guidance regarding influenza prevention and treatment.
