Five Years After the Onset of the COVID-19 Pandemic: Changing Epidemiology of SARS-CoV-2 and Seasonal Respiratory Viruses in Hospitalized Adults

Pandemic non-pharmaceutical interventions disrupted seasonal respiratory virus circulation, but longer-term pathogen-specific patterns in hospitalized adults remain incompletely defined. We evaluated detections across three nonconsecutive respiratory seasons from early relaxation of pandemic measures to five years after pandemic onset. This retrospective, observational, single-center cohort study included 2249 adults hospitalized with pneumonia, chronic obstructive pulmonary disease exacerbation, or asthma exacerbation who underwent multiplex polymerase chain reaction testing in September 2021–May 2022, September 2022–May 2023, or September 2025–May 2026. Influenza A positivity peaked in the second period (12.6%) and decreased to 6.8% in the third (p < 0.001). SARS-CoV-2 likewise peaked in the second period (9.2%) and declined to 1.5% in the third (p < 0.001). Respiratory syncytial virus increased from 0.5% in the first period to 4.9% and 3.8% in the second and third periods, respectively (p < 0.001). Positivity for other respiratory viruses did not differ (16.0%, 16.9%, and 19.1%; p = 0.308). Viral co-detection was highest in the second period (6.1% vs. 2.6% and 2.8%; p < 0.001). Respiratory virus epidemiology remained dynamic five years after pandemic onset, supporting sustained multi-pathogen surveillance.