Early and high Influenza A circulation alongside reduced Respiratory Syncytial Virus prevalence during autumn 2025 in paediatric patients attending emergency department

The recent implementation of preventive strategies against Respiratory Syncytial Virus (RSV) in infants has raised questions about potential changes in RSV seasonality and the circulation of other respiratory viruses. This study aimed to compare respiratory virus activity among paediatric patients presenting to the Bambino Gesù Children's Hospital (Rome, Italy), with respiratory symptoms and available BioFire Respiratory Panel 2.1 plus results during September-December 2024 (N = 670) and 2025 (N = 905). RSV detection decreased significantly in December 2025 compared with the same period in 2024 (6.3% vs 29.4%, risk ratio [RR]: 0.21, 95% confidence interval [CI] 0.16-0.28; p < 0.001). By contrast, influenza A viruses had an earlier onset in 2025 and emerged as the dominant pathogen compared with 2024 (21.0%, in 2025 vs 4.5%, in 2024; RR: 4.69, 95% CI 3.23-6.80; p < 0.001). Unlike September-December 2024, parainfluenza viruses (PIVs) 3 and 4 circulated in 2025 (0.4% vs 3.5% for PIV 3; 0.0% vs 3.6% for PIV-4; p < 0.001 for both), mainly observed in infants (median age 0.7 years; interquartile range: 0.2-1.2; mean±standard deviation: 0.9 ± 0.8). Circulation of adenovirus (11.5%, vs 6.1%; p < 0.001) and human coronavirus HKU1 (3.6%, vs 0.1%; p < 0.001) also increased in 2025 compared with 2024. The observed epidemiological shifts suggest potential effects associated with the introduction of RSV prophylaxis in Italy and highlight the importance of continued paediatric surveillance in monitoring evolving viral patterns and guiding public health decisions.