Presentation (CTI)

OBJECTIVES: To evaluate changes in the severity of respiratory syncytial virus (RSV) among children younger than 5 years across the pre-pandemic, pandemic, and post-pandemic periods.
METHODS: We conducted an interrupted time series (ITS) analysis using nationwide Health Insurance Review and Assessment Service claims data covering entire population in Korea from January 2009 through May 2024. The ITS model included 185 monthly observations and two interruption points: January 2020 (pandemic onset) and September 2022 (lifting of the outdoor mask mandate). Monthly intensive care unit (ICU) admissions, mechanical ventilation use, and in-hospital mortality were analyzed using negative binomial regression, whereas length of stay (LOS) was analyzed using gamma regression model. Models were adjusted for seasonality, and robust standard errors were used to account for autocorrelation.
RESULTS: At the onset of the COVID-19 pandemic, RSV severity increased abruptly, with significant immediate increases in ICU admission (IRR 5.20, 95% CI 2.08-13.01), mechanical ventilation (IRR 10.89, 95% CI 3.89-30.48), and mean LOS (+56.2%, 95% CI 3.3%-136.2%). These immediate increases were followed by significant negative changes in trend for ICU admission (IRR 0.91, 95% CI 0.87-0.94) and mechanical ventilation (IRR 0.88, 95% CI 0.84-0.92) during the pandemic period. After the transition to the post-pandemic period, ICU admission (IRR 1.08, 95% CI 1.03-1.14) showed a significant positive change in trend, whereas mechanical ventilation (IRR 4.02, 95% CI 1.06-15.21) showed a significant immediate increase. No significant changes were observed in in-hospital mortality at either intervention point.
CONCLUSIONS: The COVID-19 pandemic was associated with changes in RSV severity among children aged under 5 years, characterized by an abrupt increase at pandemic onset and dynamic trends during the pandemic and post-pandemic periods. Continued surveillance of severity is needed as RSV patterns evolve.