Effectiveness of catch-up and at-birth nirsevimab immunisation against RSV hospital admission in the first year of life: a population-based case–control study, Spain, 2023/24 season
Olivier Núñez, Carmen Olmedo, David Moreno‐Pérez, Nicola Lorusso, Sergio Fernández Martínez, Pedro Eliseo Pastor Villalba, Ángeles Gutierrez, Marcos Alonso-García, Pello Latasa Zamalloa, Rosa Sancho, Jacobo Mendioroz, Montserrat Martínez, Enriqueta Muñoz Platón, María Victoria García Rivera, Olaia Pérez‐Martínez, Rosa Álvarez-Gil, Eva Rivas Wagner, Nieves López González‐Coviella, Matilde Zornoza, María Isabel Barranco, Manuel Pacheco, Virginia Álvarez Río, Miguel Fiol Jaume, Roxana Morey Arance, Begoña Adiego Sancho, Manuel Méndez Díaz, Noa Batalla, Cristina Andreu, Jesús Castilla, Manuel Garcìa Cenoz, Ana Fernández Ibáñez, Marta Huerta Huerta, Ana Carmen Ibáñez Pérez, Belén Berradre Sáenz, J.M. Aragoneses Lamas, Luisa Hermoso, Susana Casado Cobo, Manuel Galán Cuesta, Sara Josefina Ibarra Montenegro, María de los Ángeles Díaz Domínguez, Inmaculada Jarrín, Aurora Limia, Roberto Pastor‐Barriuso, Susana Monge, the Nirsevimab Effectiveness Study Collaborators
Abstract
BackgroundRespiratory syncytial virus (RSV) causes substantial morbidity in infants < 1 year. In October 2023, Spain recommended the monoclonal antibody nirsevimab to all children born since 1 April 2023, at birth or as catch-up if born before October 2023.AimWe estimated nirsevimab effectiveness in preventing RSV hospitalisations during the 2023/24 season.MethodsWe conducted a nationwide population-based matched case-control study. Cases were children hospitalised for lower respiratory tract infection who were RSV PCR-positive. For each case, we selected four population density controls born in the same province and date (±2 days). We defined at-birth immunisation as receiving nirsevimab during the first 2 weeks of life, and catch-up immunisation within 30 days from campaign onset. Causal intention-to-treat (ITT) and per-protocol (PP) effectiveness was estimated using inverse-probability-of-immunisation weighted conditional logistic regression.ResultsWe included 406 cases and 1,623 controls in catch-up and 546 cases and 2,182 controls in at-birth immunisation studies. Effectiveness in preventing RSV hospitalisations for catch-up immunisation was 71% (95% confidence interval (CI): 65-76) by ITT and 80% (95% CI: 75-84) PP. Effectiveness for at-birth immunisation was 78% (95% CI: 73-82) by ITT and 83% (95% CI: 79-87) PP. Effectiveness was similar for ICU admission, need of mechanical ventilation, and RSV viral subgroups A and B. Children born pre-term or with birthweight < 2,500 g showed lower PP effectiveness of 60-70%.ConclusionsPopulation-level nirsevimab immunoprophylaxis in children in their first RSV season was very effective in preventing RSV hospitalisations, ICU admission and mechanical ventilation, with reduced but still high effectiveness for pre-term and low-birthweight children.