With the flu on the rise in Canada, healthcare experts are preparing for a challenging influenza season due to the global spread of an evolving H3N2 strain that may not match this year’s vaccine. Recent federal data released on Friday indicates that about two percent of nationwide tests returned positive for influenza in the previous week. While this is below the five percent threshold for Canada to declare a seasonal flu epidemic, it marks a noticeable increase from previous weeks.
The ongoing flu season in other parts of the world, particularly in the Southern Hemisphere, Asia, and the U.K., has seen record case numbers and an early onset. As Canada enters winter, it could serve as an indicator of what lies ahead. Dr. Jesse Papenburg, a pediatric infectious disease specialist at the Montreal Children’s Hospital and the McGill University Health Centre, noted that this is the second consecutive year with above-average influenza detections in the Southern Hemisphere. Last year was one of Canada’s worst influenza seasons in a decade, and there are concerns that a similar severity could be repeated this year.
In countries like Australia, the alarm has been sounded as they experienced over 410,000 lab-confirmed flu cases, marking the second consecutive year of record-high flu numbers. Similarly, the U.K. has reported a flu season starting a month earlier than usual with cases three times higher than the previous year. Parts of Asia, including Japan, have also declared a flu epidemic, leading to the closure of many schools. The early surge in these regions is speculated to be linked to a mutating H3N2 strain, known for causing severe infections, particularly in older individuals.
Dr. Danuta Skowronski, an epidemiology lead at the B.C. Centre for Disease Control, has been closely monitoring these mutations. While the H3N2 subtype has not changed significantly in recent years, it has shown more pronounced structural changes upon reaching northern countries, potentially resulting in a mismatch with the current vaccine. This season’s flu shot targets two influenza A strains (H1N1 and H3N2) and an influenza B strain.
Canadian health officials are cautious in making predictions at this stage. The Public Health Agency of Canada emphasized that data from the Southern Hemisphere may not directly predict the flu season in Canada due to varying seasonal dynamics. It is still too early to determine the severity of the upcoming flu season in Canada, which will depend on factors such as dominant influenza subtype, co-circulation of other respiratory viruses, vaccine effectiveness, and vaccine coverage.
While there is early data on the circulating influenza strains in Canada, experts anticipate a rise in H3N2 cases. Dr. Allison McGeer from Sinai Health System in Toronto warned that H3N2 seasons are usually the most severe. Older adults, particularly those aged 65 and above, are at higher risk of severe outcomes. Despite the potential mismatch with the dominant H3N2 strain, experts recommend getting the flu shot, especially for seniors.
Seasonal immunization clinics are already operational across various provinces, urging Canadians to consider getting a flu shot along with other recommended vaccines, including COVID-19 vaccines for eligible individuals. Some regions may require individuals to pay out of pocket for vaccines. Additionally, respiratory syncytial virus shots are advised for high-risk groups to prevent serious illness.