Surveillance for severe influenza, COVID-19, and RSV in patients admitted to sentinel Australian hospitals in 2025: the Influenza Complications Alert Network (FluCAN) and the Paediatric Active Enhanced Disease Surveillance (PAEDS) system.

Abstract

Introduction: Influenza, coronavirus disease 2019 (COVID-19) and respiratory syncytial virus (RSV) are common acute respiratory infections and are a cause of significant morbidity and mortality. This report summarises the epidemiology of hospitalisations with laboratory-confirmed influenza, COVID-19 and RSV in 2025 in an Australian sentinel surveillance system.

Methods: The Influenza Complications Alert Network (FluCAN) and the Paediatric Active Enhanced Disease Surveillance (PAEDS) are collaborative sentinel hospital-based surveillance programs that operate at 23 sites across all jurisdictions in Australia. Influenza, COVID-19 and RSV patients were defined as those hospitalised due to an acute respiratory infection at the sentinel hospitals with virus confirmation by nucleic acid detection.

Results: In 2025, there were 8,749 hospitalisations of patients with influenza; 3,501 with COVID-19; and 5,105 with RSV reported at the 23 sentinel hospitals. Of patients hospitalised with influenza, 4,397 (50.3%) were children (< 16 years of age); 697 (8.0%) were Aboriginal and/or Torres Strait Islander people; and 5,020 (57.4%) had chronic comorbidities. The mean length of hospital stay for patients with influenza was 4.4 days (median: 2 days). Influenza hospital admissions peaked nationally in epidemiological week 28. Influenza vaccine effectiveness against hospitalisation with any influenza type/subtype was estimated at 43% (95% confidence interval [95% CI]: 39-48%) and was highest for influenza B (75% [95% CI: 69-80%]), and lowest for influenza A H3N2 including subclade K (30.5% [95% CI: 15.0-43.2%]). Of patients hospitalised with COVID-19, 1,057 (30.2%) were children (< 16 years of age); 230 (6.6%) were Aboriginal and/or Torres Strait Islander people; and 2,544 (72.7%) had chronic comorbidities. The mean length of hospital stay for patients with COVID-19 was 7 days (median: 3 days). COVID-19 hospital admissions peaked nationally in week 26. In adults ≥ 75 years of age, the relative risk of hospitalisation was 40% (95% CI: 25-52%) lower in those who had received a COVID-19 vaccine within 180 days, compared to those vaccinated > 1 year prior to admission. Of patients hospitalised with RSV, 1,551 (30.4%) were infants (< 1 year of age) and 3,723 (72.9%) were young children (< 5 years of age); 348 (6.8%) were Aboriginal and/or Torres Strait Islander people; and 2,110 (41.3%) had chronic comorbidities. The mean length of hospital stay for patients with RSV was 3.5 days (median: 2 days). There was a peak in activity in week 28.

Discussion: Since 2022, influenza, RSV and COVID-19 have co-circulated. In 2025, disease severity-as indicated by average length of stay and proportions admitted to intensive care-was similar in patients hospitalised with any of the three pathogens. Assessment of vaccine effectiveness demonstrated protection against influenza hospitalisation and short-term protection against hospitalisation with COVID-19 in older people.