Supplementum 286: Abstracts of the annual meeting of the Swiss Society of Paediatrics (Bern, Switzerland, May 22−23, 2025)

Background: Since 2021, the RSV EpiCH project has aimed to provide representative nationwide surveillance of respiratory syncytial virus (RSV) infections in children in Switzerland.Before the COVID-19 pandemic, Switzerland experienced a stable biennial cycle of alternating strong and weak RSV winter epidemics in children.The RSV EpiCH project allowed to document the disruption of this consistent pattern during the COVID-19 pandemic with stringent implementation of non-pharmaceutical interventions.We have since observed two strong RSV seasons (2022/2023 and 2023/2024).Here, we present findings from the ongoing surveillance of RSV in children in Switzerland during the first winter season (2024/2025) in which Nirsevimab was generally available for children born after March 2024. Methods:The RSV EpiCH project prospectively collects weekly aggregated data on the detection of RSV in children from 21 of 29 paediatric acute care hospitals in Switzerland.These hospitals represent >90% of available paediatric beds in Switzerland.All sites report the number of children with detection of RSV in three age groups, <1 year old, 1 to 2 years old, and older than 2 years.We compared total patient numbers and age distribution across four time periods: 1/2021-6/2022 (2021/2022 pandemic period), 7/2022-6/2023 (winter 2022/2023), 7/2023-6/2024 (winter 2023/2024), and 7/2024-1/2025 (winter 2024/2025).Incidence rates were calculated using resident population in Switzerland in the respective age-groups. Results: From 4th January 2021 to 27th January 2025, RSV was detected in 16'058 children.5'160 (incidence rate 2.3 per 1000 children-years) in the 2021/2022 pandemic period, 5'242 (3.5 per 1000 children-years) in the winter 2022/2023, 4'672 (3.1 per 1000 children-years) in winter 2023/2024, and 984 (1.1 per 1000 children-years) in winter 2024/2025.In infants incidence rates were 23 per 1000 infants in the pandemic period, 41 per 1000 infants in winter 2022/2023, 35 per 1000 infants in winter 2023/2024, and so far 9 per 1000 infants in winter 2024/2025.In parallel, the proportion of infants amongst all RSV cases decreased from 57-61% in previous seasons to 43%, so far, in winter 2024/2025. Conclusion:In the first winter season with the general availability of Nirsevimab, preliminary data from paediatric acute care hospitals indicate that three to four times fewer infants with RSV infection are being seen in hospital.This has also led to a reduction in overall case numbers.