Nirsevimab Prophylaxis and Respiratory Syncytial Virus Hospitalizations Among Infants

Area of Science:

• Pediatrics
• Infectious Diseases
• Public Health

Background:

• Respiratory syncytial virus (RSV) is a major cause of infant hospitalizations, particularly for preterm infants and those with older siblings.
• Existing nirsevimab prophylaxis recommendations lack outcome data for high-risk infant populations.

Purpose of the Study:

• To evaluate the association between nirsevimab prophylaxis and the risk of RSV-related lower respiratory tract infection (LRTI) hospitalization.
• To assess the impact of nirsevimab on in-hospital severity of RSV LRTI among infants, including high-risk groups.

Main Methods:

• A retrospective, multicenter cohort study compared RSV seasons before and after universal nirsevimab implementation in five Italian neonatal hospitals.
• Included all live births, with follow-up until the first birthday or season end, analyzing time-to-event data.
• Used hierarchical Cox proportional hazards regression to adjust for covariates and seasonality, with sensitivity analyses.

Main Results:

• Nirsevimab prophylaxis achieved 79.2% coverage and was associated with a 68% reduction in RSV hospitalization hazard (HR, 0.32).
• Within-month analysis showed an even greater reduction in hospitalization hazard (HR, 0.11).
• Prematurity and having older siblings remained significant risk factors for hospitalization even with prophylaxis.

Conclusions:

• Nirsevimab prophylaxis substantially lowers RSV hospitalization risk and reduces in-hospital severity, supporting its public health implementation.
• Persistent risks in preterm infants and those with household exposure highlight the need for supplemental RSV prevention strategies.