Monoclonal Antibodies Show 79% Effectiveness in preventing RSV Hospitalizations in Infants
A new European study confirms the significant protective power of long-acting monoclonal antibodies against respiratory syncytial virus (RSV) in young children,offering a crucial defense during the winter respiratory virus season.
RSV is a common respiratory virus that typically causes cold-like symptoms. Though, the virus can pose a serious threat to vulnerable populations, especially infants under six months of age and adults over 65. Severe RSV infections can lead to bronchiolitis, pneumonia, and even sepsis, often requiring extended hospital stays.
As 2022,immunization products designed to prevent RSV disease have been authorized for use in the European Union. These include nirsevimab,a long-acting monoclonal antibody administered to newborns during the winter months,and vaccines for pregnant individuals to protect their infants during their first winter after birth. The European RSV season typically runs from October to April, mirroring pre-pandemic patterns.
Researchers, led by savulescu et al., recently analyzed data from Belgium, Portugal, and Spain to assess the effectiveness of nirsevimab against RSV infection during the 2024-25 winter season.Their findings, published in Eurosurveillance, demonstrate a substantial reduction in RSV-related hospitalizations among immunized infants.
The case-control study involved screening data from 4,102 hospitalized children under the age of two between September 2024 and May 2025.The analysis focused on 791 children who tested positive for RSV and 1,410 children who tested negative, serving as a control group. Children were considered immunized if they received nirsevimab between September 2024 and May 2025, regardless of dosage or age/weight at the time of management.
The study concluded that immunization with nirsevimab effectively prevented RSV-related hospitalization during the 2024-25 European winter season. The pooled overall immunization effectiveness was an extraordinary 79%, indicating a significant reduction in the risk of hospitalization due to RSV infection in this age group. As one researcher stated, “immunization of children after birth effectively prevented RSV-related hospitalization in children.”
However, the level of protection offered by nirsevimab diminishes over time. Initial effectiveness within the first month of immunization (<30 days) was 85%,decreasing to 78% between days 30 and 89,and further declining to 69% after three months (90 to 215 days) post-immunization.
Notably, the effectiveness of immunization remained high among infants aged 0-6 months – the most vulnerable age group – at 80%. the authors emphasize the need for ongoing monitoring of immunization effectiveness over time in future seasons. “Effectiveness by time since immunization needs monitoring in future seasons,” they noted.
This research provides compelling evidence for the benefits of proactive RSV prevention strategies, particularly for the youngest and most susceptible members of the population.
More data: Effectiveness of long-acting monoclonal antibodies against laboratory-confirmed RSV in children aged <24 months and hospitalised for severe acute respiratory infection,European pilot study,2024 to 2025,Eurosurveillance (2025).DOI: 10.2807/1560-7917.ES.2025.30.45.2500816
Provided by European Centre for Disease Prevention and Control (ECDC)
Citation: Monoclonal antibodies effectively prevent respiratory syncytial virus in infants (2025, November 13) retrieved 13 November 2025 from https://medicalxpress.com/news/2025-11-monoclonal-antibodies-effectively-respiratory-syncytial.html
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