Abstract

UNLABELLED: With the newly approved RSV preventive strategies enabling universal protection of infants, it is crucial to gain a comprehensive understanding of RSV hospitalization incidence, prior to the introduction of these strategies in order to facilitate an assessment of their impact. Children ≤ 2 years hospitalized with laboratory-confirmed RSV infection between 2020-2023 in France, Germany, Spain, Italy, and United Kingdom were included and compared with the 2018-2019 season. The population-based incidence was calculated as number of RSV hospitalizations divided by market share-adjusted number of children in the catchment area. Across participating countries, we observed a decrease in RSV hospitalization incidence during the 2020-2021 season due to the COVID-19 pandemic, dropping to 5.9/1000 child-years (95%CI 5.4-6.3) compared with 11.3/1000 child-years (95%CI 10.6-11.9) in 2018-2019. This decline was followed by a rebound in incidence, with rates reaching 13.8/1000 child-years (95%CI 13.0-14.5) in 2021-2022 and 18.8/1000 child-years (95%CI 18.0-19.7) in 2022-2023. Distinct patterns of RSV resurgence were observed across countries. During the 2020-2021 season, there was an increase in PICU admissions (29.5% vs 20.0% pre-pandemic, p < 0.001), despite a lower total number of RSV admissions (610 vs 1,238) compared to the 2018-2019 season. CONCLUSIONS:  The population-based incidence of RSV hospitalization in children ≤ 2 years is substantial. Considerable variation in incidence was observed between 2020 and 2023, with an initial decline during the COVID-19 pandemic followed by a rebound in the subsequent seasons. Our study underscores the importance of RSV surveillance and flexibility in RSV preventive strategies. WHAT IS KNOWN: • RSV is a major cause of hospitalization in young children under 5 years of age worldwide. • RSV seasonality was disrupted during the COVID-19 pandemic. WHAT IS NEW: • Distinct patterns of RSV resurgence were observed across five European countries during the COVID-19 pandemic, with an initial decline in incidence of RSV associated hospitalizations in children ≤ 2 years, followed by a rebound in the subsequent seasons, reaching 18.8 per 1,000 child-years (95% CI: 18.0 - 19.7) in 2022-2023.