# Nirsevimab Effectiveness Against RSV‐Related Hospitalisations in Children Under 24 Months: A Test‐Negative Case–Control Study in Portugal, 2024–2025 **Authors:** Vânia Gaio, Camila Henriques, Miguel Lança, Rita Marques, Raquel Marques, Marta Rodrigues, Sofia Almeida, Beatriz Sousa, Margarida Freitas, Diana Amaral, Sara Ferreira, Inês Azevedo, Madalena von Hafe, Rafaela Gonçalves, Regina Viseu, Teresa Bandeira, Carolina Constant, Madalena Malato, Inês Carvalho, Jorge Rodrigues, Margarida Farinha, Teresa Nunes, Teresa Graça, Sofia Gomez, Sara Soares, João Farela Neves, Paulo Paixão, Inês Piscalho, Ana Loureiro, Cristina Freitas, José Alves, Diana Soares, Paulo Lopes, Ausenda Machado, Raquel Guiomar, Ana Paula Rodrigues, Ana Carolina Pinto, Ana Carolina Pinto, Liliana Macedo, Paula Mota, Maria Francisca Santos, Carlota Ferreira, Elsa Melanie dos Santos, Ana Pinto, Tomás Tinoco, Natasha Rosário, Xavier Ferreira, Susana Maia, Inês Lopes, Vânia Soares, Arminda Jorge, Patrícia Ibarzabal, Joana Leal, Inês Couto, Beatriz Lourenço, Cláudia Fernandes, Carolina Ferreira, Bruna Barbosa, Catarina Encarnação, Rosário Barreto, Ana Sofia Santos, Marisa Nunes, Raul Martins, Ana Dias Alves, Florbela Cunha, Carla Cruz, Nádia Cavaco, Pedro Fernandes da Gama, Elsa Rocha, Cláudia Calado, Bernardo Camacho, Andreia Afonso e, Fátima Pestana, Raquel Ferreira PMC · DOI: 10.1111/irv.70186 · 2025-11-30 ## TL;DR This study found that Nirsevimab is highly effective in preventing RSV-related hospitalizations in young children in Portugal. ## Contribution The study provides new evidence on Nirsevimab's effectiveness in a predominantly healthy infant population. ## Key findings - Nirsevimab effectiveness against RSV-related hospitalisation was 78.5% (95%CI: 59.3–89.0). - Results were robust across sensitivity analyses. - Most participants were healthy infants under 2 years old. ## Abstract We assessed Nirsevimab effectiveness (NE) against respiratory syncytial virus (RSV)‐related hospitalisation in eligible children (< 2 years) using a test‐negative case–control design within the VigiRSV network (weeks 43/2024 to 16/2025). Among 341 participants (median age: 2 months; 91.2% without known chronic condition), 137 (40.2%) tested RSV‐positive. Adjusted NE against RSV‐related hospitalisation was 78.5% (95%CI: 59.3–89.0). Sensitivity analyses confirmed the robustness of the results. These findings support Nirsevimab's effect in a predominantly healthy infant population and contribute to informing public health decisions for RSV immunisation. ## Full-text entities - **Chemicals:** Nirsevimab (MESH:C000709769) - **Species:** Respiratory syncytial virus (no rank) [taxon 12814] ## Figures 2 figures with captions in the complete paper: https://tomesphere.com/paper/PMC12981484/full.md --- Source: https://tomesphere.com/paper/PMC12981484