The Canadian respiratory virus surveillance report indicates that the weekly influenza-related hospitalization rate is 2.9 per 100,000 population. “At the moment, we have not reached the peak of the influenza season, this remains data which is at the start of the epidemic. It can be much higher than that,” commented Dr. Jesse Papenburg, who works at the Montreal Children’s Hospital.
The epidemic threshold was exceeded the week ending December 21 in Canada. Since then, the curve of influenza infections has continued to rise. The epidemic threshold is 5% of positive tests for influenza. When it is exceeded and at least 15 weekly influenza detections are reported, a seasonal influenza epidemic is declared.
In Canada, the percentage of positive influenza tests in clinical laboratories is 11.3%; in Quebec, it is 10.9%, according to the most recent data from the National Institute of Public Health of Quebec (INSPQ).
Ascending phase of the epidemic
Dr Papenburg, who is a pediatrician, infectious disease specialist and microbiologist, explains that we are in the ascending phase of the epidemic. “The season has started and in the weeks that follow the incidence rates will continue to increase and we will still see many cases of influenza for the coming weeks,” he said. Usually, an influenza season can last around 10 to 16 weeks, so we still have several weeks left and we are far from the peak. I think the next few weeks are going to be more difficult in terms of influenza.”
Dr. Papenburg warns young children and the elderly who are at higher risk of complications from influenza. “Children under 5 years old, but particularly children under 2 years old, as well as our elders, people aged 65 and over, but especially 75 years and over, are at higher risk of hospitalization and complications of their influenza infection,” he says.
“I have the impression that we are going to see a typical influenza season which arrives in the middle of winter which will cause severe illness, particularly in people at higher risk,” continues Dr. Papenburg, who is also an associate member in the Department of Epidemiology, Biostatistics and Occupational Health and assistant professor of pediatrics and the Faculty of Medicine at McGill University.
Vaccination
He reminds us that there is always time to get vaccinated against influenza. Protective antibodies develop between 7 and 14 days after receiving the vaccine. “It is not too late because we are still in the ascending phase of the epidemic. The next few weeks are going to be worse than what we have right now. Someone who gets vaccinated now will offer themselves protection during this period when there is the greatest circulation of influenza.
Dr. Papenburg points out that although vaccine effectiveness varies from year to year, the average protection is 50%. In other words, getting vaccinated reduces the risk of hospitalization by half.
Influenza vaccine effectiveness estimates for the 2024-2025 season are expected to be available in February or March 2025.
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