RSV Variant Capable of Evading Nirsevimab Detected in Spain

• Three pediatric cases of a respiratory syncytial virus variant were detected in Spain during the past epidemiological season.
• The variant features the N201T substitution on the protein F, which is associated with reduced susceptibility to the monoclonal antibody nirsevimab.
• Two of the affected children had received nirsevimab and required hospital admission, including one case of severe bronchiolitis requiring pediatric intensive care unit admission and non-invasive ventilation.

Genomic Surveillance and Variant Identification

The study identified the infection as VRS-B carrying the N201T substitution on the protein F. Among the three cases registered during the past epidemiological season, two minors had received nirsevimab during that season and still required hospitalization. One patient stayed in the hospital for seven days, while the other developed severe bronchiolitis requiring a two-day stay in a pediatric intensive care unit supported by BiPAP non-invasive ventilation. The third child, who had received nirsevimab in the prior 2023-2024 season, was not hospitalized.

Researchers noted that this investigation highlights the critical role of genomic and microbiological surveillance. These findings were made possible through RELECOV, a network of microbiological laboratories across Spain’s autonomous communities that has focused on the genomic sequencing of respiratory viruses under the coordination of the CNM-ISCIII since the pandemic.

Epidemiological Context and Clinical Impact of Respiratory Syncytial Virus

Respiratory syncytial virus primarily targets infants, particularly during their first year of life, frequently leading to bronchiolitis. Epidemiological estimates indicate the pathogen affects one in four children within their first 12 months. Data show that roughly 14 percent of infected infants require medical attention, nearly 2 percent need hospitalization, and 0.1 percent require intensive care unit admission.

Infections follow a distinct seasonal pattern in Spain, typically peaking between November and January. Nirsevimab has been administered to infants since 2023 to protect against severe outcomes. Previous research published by the Instituto de Salud Carlos III demonstrated that infants under one year old immunized with the drug experience an 80 percent lower risk of hospital admission due to respiratory syncytial virus.

Research Collaborators and Prevention Strategies

The study, published in Eurosurveillance, was led by María Iglesias Caballero, Vicente Mas, and Inmaculada Casas from the Respiratory Virus Laboratory at the CNM-ISCIII, in collaboration with the University Hospital of Badajoz and the Virgen del Rocío University Hospital in Sevilla. The authors concluded that the identified genetic mutation circulates naturally and has emerged repeatedly across different viral lineages.

According to the study authors, these findings support integrating genomic surveillance with antigenic characterization to allow for the early identification and evaluation of viral variants capable of evading preventative strategies such as nirsevimab. Nirsevimab is a long-acting monoclonal antibody designed to provide single-dose protection throughout a respiratory syncytial virus season by binding to the protein F necessary for cellular entry.

Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.