Key result
RSV-B F:N201T variant reduces nirsevimab recognition and is linked to breakthrough hospitalizations in children.
Case Report (n=3)
Genomic surveillance identified sporadic emergence of RSV-B variants with the F:N201T substitution that confer reduced susceptibility to nirsevimab in children.
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Nirsevimab-treated children with RSV-B breakthroughs may harbor F:N201T variants; case data leave open population-level implications for monoclonal prophylaxis.
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.
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Iglesias‐Caballero et al. (2026) conducted a case report in RSV-B infection (n=3). RSV-B F:N201T substitution was evaluated on Hospitalization and nirsevimab recognition. Three children infected with RSV-B carrying the F:N201T substitution showed reduced nirsevimab recognition, with two requiring hospitalization despite receiving nirsevimab that season.
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