Abstract Background RSV is the leading cause of infant hospitalization, and some children with underlying conditions are at increased risk of severe RSV during their 2nd RSV season. The Advisory Committee on Immunization Practices recommends nirsevimab for U.S. children in their 2nd season with specified risk factors (Table 1). Criteria for 2nd season eligibility vary by country. Our objectives were 1) to understand the proportion of nirsevimab-eligible children and 2) to describe underlying conditions and outcomes among those not eligible in a cohort of U.S. children with severe RSV lower respiratory tract infection (LRTI). Methods We enrolled children aged 8−24 months hospitalized across 28 hospitals in 24 states with severe RSV LRTI during their 2nd RSV season during October 30, 2023–April 12, 2024, and October 1, 2024–March 31, 2025. Analytic inclusion required 1) admission to the ICU for ≥24 hours and 2) high flow nasal cannula or noninvasive (continuous positive airway pressure CPAP or bilevel positive airway pressure BiPAP) or invasive ventilation. Patient characteristics and outcomes were compared by nirsevimab eligibility status using chi-square or exact tests. Results Among 482 children with severe RSV, 33 (6%) met 2nd season nirsevimab eligibility: 5 (15%) were American Indian/Alaska Native, 24 (73%) had bronchopulmonary dysplasia (BPD) requiring ongoing medical support, one (3%) had cystic fibrosis with severe lung disease, and 3 (9%) had severe immunocompromise (Table 2). Many had other comorbidities, including 39% and 24% with cardiac and neurologic/neuromuscular disorders, respectively. Among 449 ineligible children, 151 (34%) had at least one underlying condition, and receipt of noninvasive or invasive ventilation was associated with neurologic or neuromuscular disease (p=0.048) (Table 3). Three children received nirsevimab in their 2nd RSV season, including 2 children with BPD and one with chronic lung disease and congenital heart disease. Conclusion Most children with ICU admission for severe RSV-LRTI during their 2nd RSV season were ineligible for nirsevimab. Among those who were eligible, most qualified through having BPD. One-third of ineligible children with life-threatening illness had one or more respiratory, cardiac, and neuromuscular comorbidities. Disclosures Natasha B. Halasa, MD, CSL-Seqirus: Advisor/Consultant|Merck: Grant/Research Support Adrienne G. Randolph, MD, MSc, Thermo Fisher, Inc.: Advisor/Consultant|UpToDate Inc.: Section editor, Pediatric Critical Care
Zambrano et al. (Thu,) studied this question.