P2.153: Effects of Passive Immunization on Emergency Department Presentation and Hospitalization for RSV

Background: Respiratory syncytial virus (RSV) is the most common cause of infant hospitalization1. Passive immunization (PI) strategies proven to reduce the risk of hospitalization for RSV-associated bronchiolitis include nirsevimab, a monoclonal antibody for infants, and RSVpreF vaccine for pregnant mothers. In this study, we sought to determine whether the demographic characteristics of children presenting to a pediatric emergency department (ED) with RSV or their rate of hospitalization changed following the introduction of these strategies.

Methods: We compared demographic characteristics of all children under 2 years of age who had a positive test for RSV in the Boston Children’s Hospital ED prior to the availability of PI (October 2022 – September 2023), to children diagnosed between following the initiation of PI (October 2023 – December 2024). We used multivariable logistic regression to identify factors associated with hospitalization.

Results: The study population included 2,240 infants who tested positive for RSV in the ED (Table 1). Following the availability of PI, children with RSV were older (pre-PI mean age 8.1 months, post-PI 10.9 months, p < 0.001), were more likely to be Hispanic (pre-PI 23.7%, post-PI 31.8%, p < 0.001), publicly insured (pre-PI 41.1%, post-PI 30.7%, p < 0.001), and less likely to be hospitalized (pre-PI 34.8%, post-PI 28.4%, p < 0.001) (Table 1). Across the study period, adjusted odds of hospitalization were lower among children older than 6 months (aOR 0.37, 95%CI 0.30, 0.45), of Black race (aOR 0.50, 95%CI 0.37, 0.68), and with public insurance (aOR 0.68, 95%CI 0.54, 0.84) (Table 2). However, following adjustment for these demographic factors we did not detect a significant difference in hospitalization rates following the availability of PI.

Conclusion: Post-PI, children with RSV were older and more likely to be of Hispanic ethnicity and with public insurance. The increased age of presentation suggests both significant uptake of PI in the population and that PI protects children under 6 months. However, increases in the proportions of children of Hispanic ethnicity and those with public insurance suggests the possibility of lower rates of PI within these groups, which may reflect a complex interplay of systemic barriers or cultural norms that are driving differential uptake of PI. After adjusting for demographic factors, we did not observe a significant difference in hospitalization rates for RSV+ children who presented to the ED following the initiating of PI, although we found that the likelihood of hospitalization differed by age, race, ethnicity, and insurance status across the entire study period. While lower rates of hospitalization are expected for children with RSV over 6 months compared to those under 6 months, how factors such as race, ethnicity, and insurance status influences the hospitalization rate from the emergency department for children with RSV requires further study.