(2) Nirsevimab Administration to Infants in the Neonatal Intensive Care Unit (NICU): A Single-Center Experience

Background: Nirsevimab is recommended for all infants who are discharged from the NICU during the respiratory syncytial virus (RSV) season to prevent serious RSV disease but its tolerance in high-risk infants is not well known.

Objectives: To describe the utilization and outcomes of nirsevimab usage in a level III NICU and determine the frequency of adverse events following its administration.

Design/Methods: The occurrence of apnea/bradycardia/desaturation (A/B/D) episodes in some preterm infants following nirsevimab administration prompted an observational study from 10/25/2023 to 3/8/2024 to examine potential adverse events. Specifically, occurrence of A/B/D and oral feeding (PO) percentage were determined from 3 days before to after receipt of nirsevimab. Infants who experienced A/B/D or decrease in PO ≥ 20% after nirsevimab were compared to infants who tolerated nirsevimab without A/B/D or decrease in PO. Days to discharge from nirsevimab administration was evaluated, as well as RSV readmission after discharge. Data were analyzed using Kruskal Wallis test for continuous outcomes and Fisher’s exact test for categorical outcomes.

Results: During the 2023-24 RSV season, 173/367 (47%) infants received nirsevimab before NICU discharge. Ten (6%) infants (gestational ages from 24-36 weeks) had A/B/D (n=7) or decrease in PO ≥ 20% (n=3) following nirsevimab administration. Infants who had predefined adverse event(s) did not differ from those who experienced no ill effect in birth weight, gestational age, male sex, bronchopulmonary dysplasia, maximum respiratory support during NICU stay and at time of receipt of nirsevimab. The infants also did not differ in chronologic or corrected age on the day of nirvesimab administration (Table 1). Six of the 10 infants with an adverse event also received at least one vaccine ≤ 3 days before nirsevimab (n=5 received hepatitis B vaccine, n=1 received DTaP/IPV/HEP-B/HiB and pneumococcal vaccine). Occurrence of an adverse event was associated with prolonged hospitalization. None had fever or local cutaneous reactions. One infant who tolerated nirsevimab without A/B/D or decreased PO was readmitted with RSV and COVID-19 infection.

Conclusion: Most infants tolerated nirsevimab without ill effects. However, a temporal association between receipt of nirsevimab and A/B/D and/or poor feeding occurred in 6% of infants. Monitoring of infants in the NICU after nirsevimab administration may be advisable.