With the flu on the rise in Canada, health professionals are preparing for a challenging influenza season due to the global spread of a changing H3N2 strain that may not match this year’s vaccine. Recent federal data released on Friday indicated that around two percent of tests nationwide returned positive for influenza in the past week. Although this is below the five percent threshold for Canada to declare a flu epidemic, it represents a noticeable increase from previous weeks.
The ongoing flu season in other countries, particularly in the Southern Hemisphere, Asia, and the U.K., has seen record numbers of cases and an early onset. As Canada enters the winter months, it could serve as an indicator of what lies ahead.
Dr. Jesse Papenburg, a specialist in pediatric infectious diseases at the Montreal Children’s Hospital and the McGill University Health Centre, noted that the Southern Hemisphere has experienced above-average influenza detections for two consecutive years. Last year was one of Canada’s worst flu seasons in a decade, and there are concerns that this year could be equally severe.
Australia recently reported over 410,000 lab-confirmed flu cases, marking the second consecutive year of record-breaking numbers. The U.K. also saw an early flu season with triple the number of cases compared to the previous year. Similarly, parts of Asia, including Japan, have already declared a flu epidemic, resulting in the closure of many schools.
Experts suspect that a mutated form of H3N2 is driving the early surge in flu cases. This strain is known for causing severe infections, particularly among older individuals. The concern this year is that the mutations in the virus are widening the gap between the circulating strain and the current flu vaccine.
Dr. Danuta Skowronski, an epidemiology expert at the B.C. Centre for Disease Control, highlighted that although the H3N2 subtype has remained relatively stable in recent years, it has shown significant structural changes as it spreads to northern regions. This may result in a mismatch between the virus and the vaccine.
The flu shot for this season targets two influenza A strains (H1N1 and H3N2) and an influenza B strain. Due to the virus’s variability, Skowronski emphasized that the circulating H3N2 strain differs significantly from the vaccine strain, which is a common occurrence with influenza viruses.
Canadian health officials are cautious about making predictions regarding the upcoming flu season. The Public Health Agency of Canada stated that it is too early to determine the severity of the season, as multiple factors such as dominant influenza subtype, vaccine effectiveness, and coverage will influence the outcome.
While the current data in Canada shows an equal distribution of H1N1 and H3N2 strains among detected influenza A subtypes, experts anticipate a rise in H3N2 cases. This strain is expected to lead to a dominant epidemic, affecting older adults more severely.
Dr. Allison McGeer from Sinai Health System in Toronto warned that H3N2 seasons typically result in severe flu outbreaks, especially among adults aged 60 and above. As the flu progresses, school-aged children are usually the first affected, followed by older adults who are at higher risk of severe complications.
Despite concerns about the vaccine’s match with the circulating H3N2 strain, health experts emphasize the importance of getting vaccinated, especially for Canadian seniors. Seasonal immunization clinics are operational across various provinces, encouraging residents to receive flu shots alongside other vaccines, including COVID-19 and respiratory syncytial virus shots, to protect vulnerable populations.