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Updated: Apr 15, 2026
An Improved and High Throughput Respiratory Syncytial Virus RSV Micro-neutralization Assay
Published on: January 26, 2019
Genomic surveillance of respiratory syncytial virus during 2023/2024 nirsevimab prophylaxis, Eastern Spain, early
Beatriz Mengual-Chuliá1, Cristian Launes2, Elena Cazorla3
1Virology Laboratory, Genomics and Health Area, FISABIO-Public Health, Valencia, Spain; CIBER Epidemiology and Public Health (CIBERESP), Madrid, Spain.
Insights
Nirsevimab prophylaxis for respiratory syncytial virus (RSV) in infants showed no significant emergence of resistance mutations in Spain during its first season. Ongoing genome characterization is vital for monitoring future RSV immune prophylaxis campaigns.
Area of Science:
- Virology
- Immunology
- Public Health
Background:
- Nirsevimab is a monoclonal antibody preventing RSV lower respiratory tract infections in infants.
- Spain implemented a universal nirsevimab immunization program in October 2023.
- Monitoring for viral F protein changes related to nirsevimab is crucial.
Purpose of the Study:
- To detect potential changes in the RSV F protein associated with nirsevimab prophylaxis.
- To analyze RSV genetic diversity during the first season of widespread nirsevimab use in Spain.
Main Methods:
- Whole-genome sequencing of 68 RSV isolates from infants (<1 year) in Eastern Spain (2023/2024 season).
- Isolates were categorized by nirsevimab immunization status (n=42 immunized, n=41 not) and care setting (outpatient/inpatient).
- Analysis focused on RSV clades and amino acid substitutions at nirsevimab binding sites on the F protein.
Main Results:
- RSV clade distribution varied between nirsevimab recipients and non-recipients, and between care settings.
- Limited mutations were observed at nirsevimab binding sites on the F protein, particularly in RSV-A.
- All RSV-B isolates (clade B.D.E.1) exhibited specific substitutions, irrespective of immunization status.
Conclusions:
- Nirsevimab resistance mutations have not emerged as a significant concern in Spain's first passive immunization season.
- Findings align with reports from other countries, suggesting nirsevimab's continued efficacy.
- Genome characterization of RSV is essential for monitoring prophylaxis campaigns and detecting future resistance.
Objectives:
Nirsevimab is a recombinant monoclonal antibody used to prevent lower respiratory tract infections caused by respiratory syncytial virus (RSV) in infants aged <1 year. In Spain, a universal immunization programme for all children aged <1 year has been in place since October 2023. Our goal was to detect potential changes in the viral F protein related to nirsevimab prophylaxis.
Methods:
We conducted whole-genome sequencing of 68 RSV isolates from both outpatient (n = 24) and inpatient (n = 59) infants aged <1 year, immunized (n = 42) or not (n = 41) with nirsevimab, during the 2023/2024 season in Eastern Spain.
Results:
The distribution of RSV clades and amino acid substitutions at nirsevimab binding sites on the F protein was as follows (nirsevimab recipients vs. nonrecipients): A.D.1 (35.71% [n = 15] vs. 41.46% [n = 17]), A.D.3 (9.52% [n = 4] vs. 19.51% [n = 8]), A.D.5 (16.66% [n = 7] vs. 7.32% [n = 3]), and B.D.E.1 (9.52% [n = 4] vs. 24.39% [n = 10]). Primary care versus inpatient distributions were A.D.1 (29.17% [n = 7] vs. 42.40% [n = 25]), A.D.3 (0% [n = 0] vs. 20.34% [n = 12]), A.D.5 (4.17% [n = 1] vs. 15.25% [n = 9]), and B.D.E.1 (8.33% [n = 2] vs. 20.34% [n = 12]). Small numbers precluded meaningful statistical comparisons. Only two clade A.D.3 isolates of 68 RSV-A viruses showed mutations/substitutions at nirsevimab binding sites on the F protein, one of them from a nirsevimab recipient. For RSV-B, all isolates were clade B.D.E.1 carrying three substitutions at nirsevimab binding sites (I206M + Q209 + S211N), regardless of nirsevimab immunization status or care setting.
Conclusions:
Our study presents data from Spain showing that the selection of nirsevimab resistance mutations has not emerged as a significant concern during the first passive immunization season, in line with other reports from France, the United States, and Australia. Genome characterization of RSV will be useful for monitoring immune prophylaxis campaigns and the emergence of potential resistance in the future.
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