González Sánchez, AlejandraAndrés Lacueva, Ma. CristinaPrats Méndez, IgnasiPiñana, MariaComa, ErmengolBernet Sánchez, AlbertCasañ Lopez, CristinaTorralba Calero, MiguelGutiérrez, CristinaRecio Comí, GemmaCalatayud, LauraSaubí, NarcísCreus Costa, AnnaVila, JorginaArnedo Muñoz, MariaRando, AriadnaNadal Barón, PatriciaEsperalba, JulianaBalada, EvaSoriano Arandes, AntoniAyats, JosefinaMendioroz, JacoboGonzález López, Juan JoséLarrosa, NievesPumarola, TomàsMartínez Urtaza, JaimeAntón, Andrés2025-09-152025-09-152025-08-050163-4453https://hdl.handle.net/2445/223149Objectives: To evaluate the effect of the selective pressure exerted by nirsevimab on human respiratory syncytial virus (HRSV) in Catalonia (2023-2024) by analysing viral mutations, diversity, and evolutionary dynamics, based on viruses characterised from non-immunised and previously immunised patients. Methods: Respiratory samples were collected through the SIVIC sentinel network and three hospitals in Catalonia. HRSV-positive samples underwent whole-genome sequencing (WGS), or F gene sequencing when WGS was not feasible. Viral diversity, phylogenetics, and selection pressure were assessed. Results: A total of 251 WGS (HRSV-A: 165; HRSV-B: 86) and 27 F gene sequences (HRSV-A: 13; HRSV-B: 14) were obtained for the non-immunised group. For immunised cases, 79 WGS (HRSV-A: 67; HRSV-B: 12) and 12 F sequences (HRSV-A: 10; HRSV-B: 2) were analysed. Lineage distribution remained similar between groups. Nucleotide diversity was similar for HRSV-A groups, though reduced in immunised HRSV-B. Selection pressure analyses suggested a shift toward neutral evolution in immunised samples. Mutations N63S, K65R, I206T , K209E (HRSV-A) , K68E, R209Q, and S211N (HRSV-B) were detected in nirse- vimab epitope, with K209E and K68E absent in non-immunised samples. Conclusions: Nirsevimab immunisation may influence HRSV evolution, particularly in HRSV-B. Continued genomic surveillance is crucial for early mAb-resistant mutants detection. (c) 2025 Published by Elsevier Ltd on behalf of The British Infection Association. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).10 p.application/pdfengcc by-nc-nd (c) González Sánchez, Alejandra et al, 2025http://creativecommons.org/licenses/by-nc-nd/3.0/es/ImmunoteràpiaEpidemiologia molecularImmunotheraphyMolecular epidemiologyinfo:eu-repo/semantics/article2025-09-10info:eu-repo/semantics/openAccess40769426