Health conditions and RSV-related Pediatric Intensive Care Unit admissions in children during their second RSV season

Importance: Respiratory syncytial virus (RSV) hospitalization rates are highest among children <2 years of age. RSV immunization with infant monoclonal antibody or maternal vaccine is recommended to protect all U.S. infants in their first RSV season. For certain high-risk children aged 8-19 months entering their second RSV season, the monoclonal antibody nirsevimab is recommended. Little is known regarding preexisting health conditions as risk factors for RSV-associated respiratory failure in children during their second season. Objectives: To describe children admitted to the pediatric intensive care unit (PICU) for RSV during their second RSV season by preexisting health conditions, and to compare demographic and clinical characteristics across groups. Design, Setting, and Participants: Surveillance registry of children 8- <24 months old admitted to the PICU in 30 pediatric hospitals in the 2023-2024/2024-2025 RSV seasons. All children had an RSV-positive respiratory sample and received respiratory support with high flow nasal cannula, noninvasive ventilation, or invasive mechanical ventilation (IMV). Exposure: Preexisting health conditions potentially increasing risk of severe RSV disease. Main Outcomes and Measures: Patients were classified into four mutually exclusive groups by preexisting health conditions: 1) U.S. nirsevimab eligible criteria, 2) other identified RSV risk conditions (with some evidence of increased risk for severe RSV), 3) other preexisting conditions, and 4) no preexisting conditions. Patient demographic characteristics and level of respiratory support received were compared. Results: Among 574 children: 47 (8.2%) had U.S. nirsevimab eligibility criteria, 76 (13.2%) had other RSV risk conditions, 96 (16.7%) had other preexisting conditions, and 355 (61.8%) had none. A higher proportion of children with nirsevimab eligibility factors (40.4%) than those with other identified RSV risk conditions (17.1%) required IMV, which was higher than other (10.4%) or no (5.9%) preexisting health conditions (ptrend<0.001). Conclusions and Relevance: Approximately 20% of children admitted to the PICU with severe RSV were in the defined groups that met U.S. nirsevimab-eligibility criteria or that had an identified RSV risk condition associated with known risk for severe RSV. A considerable proportion of both groups of children required IMV for respiratory support. These findings may help inform future deliberations regarding U.S. second season nirsevimab-eligibility recommendations.