María Iglesias-Caballero, Jose A Infantes, Albert Campoy, Sara Camarero-Serrano, Silvia Moreno, Olga Cano, Germán Vallejo-Palma, Carmen González-Velasco, Cristina Gaona, Pedro Camacho-Martinez, Laura Merino-Diaz, Sonia Vázquez-Morón, Francisco Pozo, Jose A Lepe, Vicente Mas, Inmaculada Casas
During Spain's 2025/26 RSV season, three children were infected with RSV-B viruses carrying the F protein N201T substitution. Two who received nirsevimab that season were hospitalised (one required intensive care); the third was treated previously. Recombinant expression studies confirmed reduced nirsevimab recognition. Genomic data indicated sporadic emergence across distinct RSV-B backgrounds rather than expansion of a single lineage. Findings highlight the importance of combining genomic surveillance with antigenic characterisation to detect and interpret variants with reduced susceptibility to antibody-based prevention.