Normalization of Seasonality and Age Distribution of Pediatric RSV Infection Following the Pandemic Disruption in the Netherlands

BACKGROUND: The COVID-19 pandemic caused a global disruption in respiratory syncytial virus (RSV) epidemiology. However, data on RSV epidemiology in the postpandemic period remain limited. We analyzed shifts in RSV seasonality, age distribution, and disease severity among RSV-positive children in the Netherlands before, during, and after the pandemic.

METHODS: Between May 2021 and April 2024, children under two years of age, admitted with RSV to 47 Dutch hospitals were included in a prospective surveillance study. We compared demographic and clinical characteristics of RSV-positive patients with data from the pre-COVID period (2018-2020), the COVID period and the post-COVID period (2022-2024).

RESULTS: A total of 8457 RSV-positive cases were included, with detailed data collected from 2708 patients (13 hospitals). Following an unusual off-season shift and a period of endemic circulation, RSV seasonality has reverted to its typical prepandemic winter pattern. The median age at admission increased from 2.2 months (interquartile range [IQR]: 1.1-5.6) in the prepandemic period to 4.9 months (IQR 1.8-11.4, P < .05) during the summer outbreak (2021). This subsequently returned to prepandemic median age in the winter of 2023/2024 (2.7 months, IQR 1.3-8.0, not significant). We observed no differences in the prevalence of preterm birth or comorbidities among RSV-positive children before, during or after the COVID pandemic.

CONCLUSIONS: The COVID-19 pandemic profoundly disrupted RSV epidemiology. This prospective study demonstrates a rapid re-establishment of prepandemic patterns, including a return toward the typical age distribution during early childhood.