Start of Influenza Season Declared in Ottawa
To: Ottawa Physicians, Nurse Practitioners and Midwives
Date: November 12, 2026
From: Dr. Alysha Ahmed, Associate Medical Officer of Health
Subject: Start of Influenza Season Declared in Ottawa
Dear Colleagues:
Ottawa Public Health (OPH) has declared the start of the 2026-2027 influenza season in Ottawa as of October 31, 2026.
Influenza season is declared when the percent positivity for influenza exceeds 5% for two consecutive weeks. For the week ending October 31, 2026, the percentage of respiratory lab specimens positive for influenza was 6.6%. The week prior, the percentage of respiratory lab specimens positive for influenza was 5.3%.
Most recently, for the week ending November 7, 2026, percent positivity for influenza was 6.1%. In addition to a rising proportion of tests positive for influenza, hospitalizations for influenza have also been increasing.
Influenza Epidemiology- 2026-2027 Respiratory Season to Date
- A total of 253 laboratory-confirmed influenza cases have been reported in Ottawa to date this season. Of these cases, 98.8% (250/253) have been influenza A.
- Provincially and nationally, the majority of influenza cases to date are influenza A with some influenza B cases also reported, as is typical during the early flu season. To date, influenza A(H1N1) is the dominant subtype among sub-typed influenza A specimens.
Influenza Vaccine Effectiveness & Strain Characterization
- Initial estimates of influenza vaccine effectiveness in Canada typically aren’t available until later in the season.
- Influenza genetic characterization results from the National Microbiology Lab (NML) show that 97.8% (90/92) of characterized H1N1 samples are subclade D.3.1.1.
- All H1N1 isolates antigenically characterized at NML this season have had similar reactivity to the vaccine strain, demonstrating good vaccine-to-circulating strain match.
- Vaccination remains a key tool for protection against influenza A and B, including severe outcomes from influenza.
Influenza Resources
- A summary of influenza resources for health care professionals can be found on OPH’s Influenza for Health Care Professionals webpage; information on fall respiratory vaccines (influenza, COVID-19, and RSV) can be found in OPH’s recent Public Health Alert.
- Ontario Health provides guidance on influenza antiviral therapy and post-exposure prophylaxis on their Influenza Resourceswebpage.
- Up-to-date local respiratory surveillance is available at OttawaPublicHealth.ca/VirusReport.
- Resources for patients and their families can be found at OPH’s Influenza (Flu) Vaccines webpage.