Infants protected with nirsevimab, a new monoclonal antibody, experienced significantly fewer hospitalizations due to respiratory syncytial virus (RSV) compared to those whose mothers received an RSV vaccine during pregnancy, according to a recent study conducted in France. The findings, published in JAMA, offer an early real-world comparison of two strategies aimed at safeguarding infants against severe RSV illness, a common and potentially dangerous respiratory infection. Here’s particularly relevant as RSV is a leading cause of hospitalization in infants under one year old, and the availability of preventative measures is relatively new.
The study, which analyzed data from over 42,000 infants, comes at a crucial time. For decades, there was no approved preventative treatment for RSV. In the past year, however, both maternal vaccines and infant monoclonal antibodies like nirsevimab have become available, offering new avenues for protection. Understanding how these approaches compare in effectiveness is vital for public health officials and clinicians making recommendations to families. The Centers for Disease Control and Prevention (CDC) recommends nirsevimab for all infants younger than 8 months during their first RSV season, and for some older infants who are at increased risk of severe illness. More information on RSV and prevention can be found on the CDC website.
Researchers from France utilized data from the French National Health Data System, focusing on infants born between September 1 and December 31, 2024. The cohort was divided into two groups of 21,280 infants each, carefully matched based on factors like maternity ward discharge date, sex, gestational age, and region. The average age of infants at the start of the study was 3.7 days, and they were followed for a median of 84 days. This rigorous matching process helps to ensure that any observed differences between the groups are likely due to the preventative intervention—either nirsevimab or maternal vaccination—rather than pre-existing differences between the infants.
Nirsevimab Demonstrates a Clear Benefit in Reducing Severe RSV Outcomes
The study recorded 481 hospitalizations related to RSV-associated lower respiratory tract infections across the entire cohort. However, a notable difference emerged between the two groups: 212 hospitalizations occurred in the nirsevimab group, compared to 269 in the group whose mothers received the RSVpreF vaccine. This translated to an adjusted hazard ratio of 0.74, indicating a 26% reduction in the risk of RSV-related hospitalization for infants receiving nirsevimab. A hazard ratio is a measure of relative risk; a value less than 1 suggests a lower risk in the intervention group.
The benefits of nirsevimab extended beyond simply reducing hospitalizations. Infants who received the monoclonal antibody also experienced lower rates of more severe complications. The adjusted hazard ratio for admission to the pediatric intensive care unit (PICU) was 0.58, meaning a 42% reduction in risk. Similarly, the risk of requiring ventilator support was reduced by 43% (hazard ratio 0.57), and the need for oxygen therapy decreased by 44% (hazard ratio 0.56). These findings suggest that nirsevimab not only prevents milder cases of RSV but also offers substantial protection against the most serious manifestations of the disease.
Comparing Prevention Strategies: Maternal Vaccination vs. Passive Immunization
The two preventative strategies differ in their approach. Maternal vaccination, using the RSVpreF vaccine (such as Arexvy, approved by the FDA in May 2023 according to the FDA), aims to generate antibodies in the mother that are then passed on to the fetus, providing passive immunity to the infant. Nirsevimab, is a laboratory-produced antibody directly administered to the infant, providing immediate, though temporary, protection. This is known as passive immunization.
The French study suggests that, at least in this setting, passive immunization with nirsevimab offers a more robust level of protection against severe RSV disease. However, it’s important to note that this is an early comparison, and the long-term effects of both strategies are still being evaluated. The study focused on a specific population in France, and the results may not be directly generalizable to other regions or populations. Factors such as circulating RSV strains and healthcare access could influence the effectiveness of each approach.
Looking Ahead: Continued Monitoring and Research
The authors of the study emphasize the need for ongoing evaluation as both nirsevimab and maternal RSV vaccines become more widely used. Further research is needed to understand how these strategies perform in different populations, over multiple RSV seasons, and in combination with other preventative measures. The study’s findings are consistent across various subgroup analyses, bolstering confidence in the observed associations, but continued monitoring is essential.
For clinicians, this study provides valuable early data to inform their recommendations to parents. While both strategies aim to reduce the burden of RSV, the current evidence suggests that nirsevimab may offer a more significant reduction in hospitalization and severe outcomes. The decision of which preventative approach to employ should be made in consultation with a healthcare provider, taking into account individual risk factors and local guidelines.
Disclaimer: This article provides information for general knowledge and informational purposes only, and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
The next major update on RSV prevention strategies is expected from the CDC’s Advisory Committee on Immunization Practices (ACIP) during their meeting in February 2025, where they will review new data and potentially update their recommendations. Stay informed and discuss your options with your pediatrician to ensure your child receives the best possible protection against RSV. Share this article with your network to help spread awareness about these important advancements in infant health.
