470 - Beyfortus Administration in Inpatient Neonates ≥35 Weeks Corrected Gestational Age in a Quaternary Care Neonatal and Infant Critical Care Unit

Publication Number: 2458.470

Sarah N. Carpenter, Children's Hospital Los Angeles, Los Angeles, CA, United States; Rebecca Martinez-Hannon, Children's Hospital of Los Angeles, Los Angeles, CA, CA, United States; Lilly Yen, Childrens Hospital Los Angeles, Los Angeles, CA, United States; Troy Zeier, Children's Hospital Los Angeles, Los Angeles, CA, United States

Background: RSV preventive antibody Nirsevimab (trade name Beyfortus) prevents RSV-related lung disease, the most common cause of bronchiolitis and pneumonia in children under 1 year. While Beyfortus is safe to give with other routine vaccines, this is a relatively new approach to RSV prevention since its approval by the FDA in August 2023. Currently the guidance provided on Beyfortus administration is to administer to all healthy infants < 8 months old during their first RSV season (October-March) and to high-risk populations > 8 months old during their second RSV season. There is minimal guidance at what corrected gestational age to administer Beyfortus to former premature infants, and minimal guidance on benefit of administration in patients that are anticipated to remain inpatient during RSV season.

Objective: Demonstrate the safety and efficacy of administering Beyfortus to stable patients ≥35 weeks corrected gestational age admitted in a level IV Neonatal and Infant Critical Care Unit (NICCU), regardless of anticipated discharge.

Design/Methods: We conducted a retrospective chart review describing Beyfortus administration in Level IV NICCU patients ≥35 weeks corrected gestation that were deemed medically stable while inpatient across two seasons (October 2023-March 2024 and October 2024-March 2025). Redcap data was used to document demographic information, diagnoses, adverse reactions to Beyfortus, and concurrent routine vaccination administration. We used Chi-square tests to compare proportions for categorical variables and Kruskal-Wallis rank sum tests for continuous variables. All data analyses were conducted using R.

Results: Table 1 shows patient demographics for those who qualified for Beyfortus in the 2023-2024 and 2024-2025 RSV seasons. Table 2 shows percentage of patients who received Beyfortus in both seasons with 17% and 25.8% respectively. For 2023-24 the median gestational age at birth was 37w4d and corrected gestational age at administration was 42w4d and for 2024-25 was 36w1d and 42w4d respectively. Also shown are adverse reactions. Table 3 shows documented reasons for not receiving Beyfortus.

Conclusion(s): Beyfortus is safe to administer inpatient at ≥35 weeks corrected gestational age in stable NICCU patients. Based off our findings, it is safe to administer other routine childhood immunizations concurrently with Beyfortus in admitted NICCU patients. There were no major adverse reactions noted. For the 2025-2026 RSV season our administration criteria will remain the same with consideration of administration at ≥34 weeks corrected gestational age.

Table 1. Demographic Characteristics of Study Patient Population (2023-2024 vs 2024-2025)
† Other diagnoses included airway anomaly, congenital diaphragmatic hernia, disorder of the GI tract, ECMO, genetic disorder, hyperbilirubinemia, meconium aspiration, neonatal encephalopathy, neurologic disorder, serious bacterial infection, and viral infection.

Table 2. Summary of Beyfortus Administration (2023-2024 vs 2024-2025)
† Other diagnoses included airway anomaly, congenital diaphragmatic hernia, disorder of the GI tract, ECMO, genetic disorder, hyperbilirubinemia, meconium aspiration, neonatal encephalopathy, neurologic disorder, serious bacterial infection, and viral infection.

Table 3. Reasons Patients Did Not Receive Beyfortus (2023-2024 vs 2024-2025)
† Other reasons cited for not receiving Beyfortus include shortage of Beyfortus doses and incorrect thought that Beyfortus was contraindicated in active RSV infection.