Summary
What is already known about this topic?
Vaccines for maternal respiratory syncytial virus (RSV) and nirsevimab—a long-lasting monoclonal antibody—help prevent hospitalizations in infants due to RSV, becoming widely accessible in the U.S. during the 2024–25 RSV season.
What is added by this report?
This analysis compared hospitalization rates for infants aged 0–7 months during the 2024–25 RSV season to rates from pre–COVID-19 pandemic seasons in two surveillance networks. It found a reduction in hospitalization rates of approximately 28% to 43% for this group.
What are the implications for public health practice?
The 2024–25 RSV season marked the first with broad availability of the new vaccine and nirsevimab, showing lower hospitalization rates among infants compared to earlier seasons. Effective healthcare strategies should prioritize the protection of infants early in the RSV season through maternal vaccination or nirsevimab administration.
Abstract
The 2024–25 RSV season saw widespread use of a maternal RSV vaccine and nirsevimab aimed at preventing severe RSV disease in young children. This report evaluated how the introduction of these products affected hospitalization rates for RSV among infants and young children. Compared to data from the 2018–20 RSV seasons, infants aged 0–7 months experienced significant reductions in hospitalization rates, estimated at 43% and 28% respectively. The largest declines were observed in those under 2 months of age and during peak hospitalization months. These findings underscore the need for early protection through vaccination strategies, ideally right before birth or within the first week of life.
Introduction
Respiratory syncytial virus (RSV) stands as the primary cause of hospitalization among infants in the U.S., particularly affecting those aged 0–2 months. Two preventative measures—maternal RSV vaccines and nirsevimab—were initiated in the 2023–24 RSV season to protect these vulnerable groups. This analysis examined hospitalization rates before and during the 2024–25 season using data from surveillance networks.
Methods
Data Sources
The RSV-Associated Hospitalization Surveillance Network (RSV-NET) engaged in active surveillance for lab-confirmed RSV hospitalizations, while the New Vaccine Surveillance Network (NVSN) monitored acute respiratory illness among hospitalized children. This analysis utilized data for children under 5, comparing the 2018–20 RSV seasons with the most recent season, excluding atypical seasons influenced by the pandemic.
Data Analysis
Hospitalization rates for groups receiving potential RSV prevention products were analyzed. Rates were calculated using population estimates, and adjustments were made to account for potential underreporting of RSV cases. A sensitivity analysis was performed to enhance the reliability of findings.
Results
Characteristics of Children Hospitalized for RSV
A total of 18,389 RSV-associated hospitalizations were recorded for children under 5 years, revealing significant reductions in the 2024–25 season versus earlier years. The median ages of hospitalized children varied across seasons.
RSV-Associated Hospitalization Rates Among Infants Aged 0–7 Months
Hospitalization rates for infants aged 0–7 months significantly dropped during the 2024–25 season compared to 2018–20 rates, especially for the youngest infants, indicating that preventive measures like vaccination are essential for this high-risk group.
RSV-Associated Hospitalization Rates Among Older Children
In contrast, hospitalization rates among older age cohorts (8–19 months and 20–59 months) were higher in 2024–25 compared to the previous years, suggesting a more severe RSV season overall.
Discussion
The 2024–25 season marked the first with significant adoption of maternal RSV vaccines and nirsevimab. Analyses indicated a notable decrease in hospitalization rates for infants, which implies that these preventive measures are effective. However, elevated rates in older children suggest that the drop in infant hospitalizations might be miscalculated due to varying factors unrelated to the introduction of preventive products.
Limitations
This analysis has several limitations including the ecological study design, which does not allow for direct causal interpretations, and potential underdetection in hospitalization reporting. Additionally, the catchment areas of the surveillance networks may not represent national demographics.
Implications for Public Health Practice
This season showed reduced hospitalization rates among infants, underscoring the need for well-planned healthcare strategies that promote timely use of preventive measures to protect infants as soon as possible during RSV seasons. Recommendations support maternal vaccination or nirsevimab for newborns during their first week of life.
Acknowledgments
Thanks to the investigators and partners involved in the respiratory syncytial virus surveillance networks.
