Epidemiological Changes in Pediatric RSV Infections in Poland (2016-2024): Impact of the COVID-19 Pandemic

Objective: The COVID-19 pandemic disrupted the seasonal pattern of RSV infections, increasing cases outside the typical epidemic season. This study aimed to assess the pandemic's impact on the clinical characteristics of RSV infections in children hospitalized at the Polish Mother's Memorial Health Institute in Łódź, based on a 9-year observation period from 2016 to 2024. Methods: A retrospective analysis was conducted on 330 children hospitalized for RSV between 2016 and 2024. Patients were divided into pre-COVID-19 (2016-2020, n = 160) and post-COVID-19 (2021-2024, n = 170) groups. The hospitalization course, the treatment duration, the use of oxygen, antibiotics, systemic steroids, the patient age structure, and risk factors were compared. Results: Following the pandemic, the age profile of hospitalized RSV patients shifted, with more children over 12 months (27% post-COVID-19 vs. 18% pre-COVID-19). RSV hospitalizations increased as COVID-19 cases declined (correlation coefficient: -1.0; p < 0.001). The average hospitalization duration decreased by 1.8 days (p = 0.002). Oxygen therapy was used more frequently post-pandemic (p < 0.001), while antibiotic use decreased (51.75% vs. 81.25%; p < 0.001). No significant difference was observed in ICU transfer rates. Premature infants and children with congenital defects experienced longer hospitalizations, with a stronger correlation noted post-COVID-19 (0.38; p < 0.001). Conclusions: The COVID-19 pandemic changed the profile of children hospitalized with RSV, increasing the proportion of older patients. Despite shorter hospital stays, prematurity and congenital anomalies remained key risk factors for severe disease. Study limitations include its retrospective design, selection bias, and limited socio-demographic and clinical data due to pandemic-related constraints.