P-1186. Significant Reduction in Disease Burden and a Shift in Clinical Diagnoses in Children Hospitalized with Respiratory Syncytial Virus (RSV) after Nirsevimab Implementation in Catalonia (Spain)
Authors: Creus-Costa Anna , Piñana Maria , Perramon-Malavez Aida , Andrés Cristina , Rello-Saltor Victòria , Rossich-Verdés Romy , Carsi-Durall Ariadna , Cañadas-Palazón Sonia , Tobeña-Rué Marc , González-Peris Sebastià , Sancosmed-Ron Mónica , Rodrigo-García Rocío , Rodríguez-Losada Olalla , Lera-Carballo Esther , Wörner-Tomasa Núria , Casquero-Cossío Alejandro , Vidal-Moreso Anna , Lobato Zulema , Pujol-Soler Berta , González Iris , López Núria , Ruiz-García Montserrat , Flores Sergio , Rius Neus , Visa-Reñé Núria , Geronès Laura , Mejias Asuncion , Balcells Joan , Soler-Palacín Pere , Prats Clara , Vila Jorgina , Antón Andrés , Soriano-Arandes Antoni 
Published: January 2025

Abstract

Background
RSV causes a significant burden including hospitalization in infants. Nirsevimab prophylaxis was implemented in October 2023 in Catalonia (Spain) for all children &lt; 6-months-old to reduce RSV-associated morbidity. We aimed to define the impact of nirsevimab administration on clinical outcomes of hospitalized children with RSV infection.

Methods
We compared clinical data from RSV-associated hospitalizations in children &lt; 16-years-old between October 2022 - March 2023 and October 2023 - March 2024. Respiratory samples were collected from 11 hospitals of the COPEDICAT network (https://www.copedicat.cat). Laboratory confirmation was performed by a real-time multiplex RT-PCR-based assay (Allplex Respiratory Panel Assay, Seegene, South Korea) or antigen test. Disease severity was defined by the pulmonary score and/or need for PICU care.

Results
We included 636 hospitalized patients (63.5% in 2022-23 and 36.5% in 2023-24), mostly with lower respiratory tract infections (97.6%). Median age in the 2022-23 season was 4.5 vs 11 months in the following season (p&lt; 0.001). The proportion of children &lt; 6-months-old was also significantly lower in 2023-24 (53.0% vs 31.5%, p&lt; 0.001) (Figure 1). There was a 42.6% reduction in hospitalizations in 2023-24 compared with the previous season; most of the hospitalized children in the 2023-24 season had not been immunized with nirsevimab (72.5%). In 2023-24, there was a higher proportion of bronchitis (40.1% vs 27.2%, p&lt; 0.001) and children treated with bronchodilators and corticosteroids (both p&lt; 0.001) compared to the previous season. The number of PICU admissions decreased by half (60 vs 32), but its percentage in relation to total hospital admissions did not change significantly (14.9% vs 13.8%, p=0.58). No significant differences were found in the clinical score at admission or respiratory support.

Conclusion
After the introduction of nirsevimab in infants &lt; 6-months-old, children admitted to catalan hospitals were older and the proportion of bronchitis was significantly higher than in the previous season. In addition, there was a reduction of almost 50% RSV-associated hospitalizations and PICU admissions compared to the previous season; most of the hospitalized children had not been immunized with nirsevimab.

Disclosures
Asuncion Mejias, MD, PhD, MsCS, Astra-Zeneca: Advisor/Consultant|Astra-Zeneca: Honoraria|Enanta: Advisor/Consultant|Janssen: Advisor/Consultant|Janssen: Grant/Research Support|Merck: Advisor/Consultant|Merck: Grant/Research Support|Moderna: Advisor/Consultant|Pfizer: Advisor/Consultant|Pfizer: Honoraria|Sanofi-Pasteur: Advisor/Consultant|Sanofi-Pasteur: Honoraria