Ontario Respiratory Virus Tool

Key findings for the 2025-26 surveillance period (August 24, 2025 to March 28, 2026)

Influenza: The 2025–26 respiratory virus season saw an early and intense period of influenza activity. Percent positivity exceeded 5% in mid‑November and peaked at 35.7% in mid‑December. Influenza A drove activity, with A/H3N2 (primarily subclade K) predominating. The highest percent positivity was observed among children aged 5–11 years, followed by those aged 12–19 years, and activity began and peaked earlier in these age groups. Influenza B activity increased later in the season but remained low, with the highest positivity also among school‑aged children. Although weekly cases, hospital admissions, and outbreaks were higher than in recent seasons during the peak, the shorter duration of activity resulted in totals for these measures that were similar to or lower than 2024–25.

COVID‑19: COVID‑19 activity remained low throughout the 2025–26 season. Percent positivity peaked at 9.7% in mid‑September. Overall, percent positivity, cases, outbreaks, hospital admissions, and deaths were lower than in all previous seasons.

RSV: RSV activity began later than in recent seasons, peaking at 7.9% in February before declining. Children under five years of age had the highest percent positivity, with activity starting and peaking earlier in this group. Maximum weekly RSV percent positivity, outbreaks and hospital admissions were lower than in recent seasons. However, the overall period of RSV activity was longer than in the past.