New RSV Vaccine and Treatment Reduce Infant Hospitalizations
Respiratory syncytial virus (RSV) has long been the leading cause of hospitalization among infants in the United States, with an estimated 58,000 to 80,000 children under five admitted each year. However, new data released by the Centers for Disease Control and Prevention (CDC) for the 2024–2025 RSV season shows a dramatic reduction in infant hospitalizations following the rollout of two novel preventive measures: Pfizer’s maternal vaccine Abrysvo and the long-acting monoclonal antibody nirsevimab.
Key Findings from the 2024–2025 RSV Season
- Newborns (0–2 months) saw a 52 percent decline in hospitalizations in the RSV-NET surveillance network and a 45 percent drop in the NVSN network compared with the 2018–2020 pre-pandemic baseline.
- Excluding early-season data from Houston, where RSV circulation began before product rollout, NVSN reported a 71 percent decline in newborn admissions.
- Infants aged 0–7 months experienced a 43 percent hospitalization reduction in RSV-NET and a 28 percent reduction in NVSN; excluding Houston boosted the NVSN drop to 56 percent.
- Toddler and child (up to 5 years) hospitalization rates rose compared with pre-pandemic years, suggesting an overall more severe RSV season and reinforcing that infant declines likely understate the true impact of new interventions.
Mechanism of Action and Immunogenicity
Abrysvo is a bivalent prefusion F protein subunit vaccine formulated with a proprietary lipid-based adjuvant that enhances dendritic cell uptake and drives robust neutralizing antibody titers. When administered to pregnant people during the third trimester (ideally between 32 and 36 weeks gestation), maternal immunoglobulin G (IgG) crosses the placenta via the neonatal Fc receptor (FcRn), conferring passive immunity to the fetus lasting the first three to five months of life.
Nirsevimab, developed by AstraZeneca and Sanofi, is a human monoclonal antibody directed against the prefusion conformation of the RSV F protein. Engineered for an extended half-life of approximately 70 days through Fc engineering (YTE mutation), a single intramuscular dose at birth or at season onset maintains protective serum concentrations (>40 µg/mL) throughout the 5-month RSV season.
Public Health Impact and Coverage
Early uptake data from CDC and state immunization registries indicate that approximately 60 percent of eligible pregnant people received Abrysvo during the 2024 fall immunization window, while nirsevimab coverage among infants under eight months reached 45 percent by December 2024. Modeling studies suggest that increasing combined coverage to 80 percent could prevent up to 35,000 additional hospital admissions and save an estimated 125 million dollars in direct medical costs annually.
Dr. Alicia Nguyen, lead epidemiologist at the CDC Respiratory Virus Division, commented, “Our real-world data confirms that maternal vaccination and long-acting prophylaxis are complementary strategies. By targeting both prenatal and neonatal populations, we can effectively bridge the immunity gap in the first critical months of life.”
Future Directions and Research Gaps
While these interventions represent a major public health breakthrough, several questions remain. Ongoing Phase 4 studies are evaluating the durability of Abrysvo-derived antibodies beyond six months post-birth and assessing safety in diverse demographic cohorts. Additionally, next-generation monoclonal candidates targeting both RSV A and B subtypes are in preclinical development, aiming to further broaden protection and address antigenic drift.
Integration with maternal immunization programs for influenza and Tdap presents logistical challenges that health systems must address. Electronic health record alerts and bundled prenatal care visits could enhance timely administration. Moreover, cost-effectiveness analyses in low-resource settings will be crucial as global health agencies consider wider deployment.
Conclusions and Expert Perspectives
- Combined use of Abrysvo and nirsevimab led to unprecedented reductions in infant RSV hospitalizations during the 2024–2025 season.
- Evidence supports scaling up coverage to maximize public health benefits and cost savings.
- Future research should focus on long-term immunogenicity, broad-spectrum prophylaxis, and implementation strategies.
As RSV remains a major threat to pediatric health worldwide, these innovative biologics mark a turning point in preventive care. Continued surveillance, rigorous clinical evaluation, and coordinated immunization policies will be essential to sustain and expand these gains.