Effectiveness of abrysvo and nirsevimab in preventing RSV

Objectif(s) de la recherche et intérêt pour la santé publique

Finalité de l'étude

Objectifs poursuivis

Domaines médicaux investigués

Bénéfices attendus

This study will provide public health data on the comparison of effectiveness of passive immunization (abrysvo, nirsevimab) in preventing RSV-related LRTI in children, in order to guide public health strategies for addressing this severe disease, responsible for a major morbidity and mortality.
This is a population-based retrospective cohort design study using data from the SNDS (SNIIRAM+ PMSI+ Causes médicales de décès) collected between September 2024 and August 2025 in the pediatric population.
Study outcomes among infants born to abrysvo-vaccinated mothers (exposed group) will be compared with those among infants vaccinated with nirsevimab (comparison group) initially from birth through 6 months of age, with other outcomes assessed from birth through 6 months, as the infants reach this age and their data become available. This study seeks to assess the impact of national RSV program introduction in France by examining incidence rates of hospitalizations for RSV-associated LRTI over time.

Primary Objective: assess the effectiveness of passive immunization with abrysvo or nirsevimab in preventing RSV-related LRTI in children up to 6 months in France.
Secondary Objectives:
• To assess the effectiveness of passive immunization with abrysvo and nirsevimab in preventing RSV-related LRTI requiring pediatric intensive care unit (PICU) admission.
• To assess the effectiveness of passive immunization in preventing RSV-related LRTI according to birth weight (low birth weight; normal birth weight)
• To assess the effectiveness of passive immunization in preventing RSV-related LRTI according to need for invasive/non-invasive ventilation (yes/no)
• To assess the effectiveness of passive immunization in preventing RSV-related LRTI according to diagnosis (pneumopathies; bronchiolitis/bronchiolitis)
Using matched participants’ socio-demographic characteristics and comorbidities (FDep, gestational age, chronic lung disease, congenital heart disease/congenital heart defects and diseases, immune-deficiencies, neuromuscular impairment, chronic lung disease, trisomy 21, bronchopulmonary dysplasia, neonatal respiratory distress, anomalies of the nervous system, chromosomal abnormalities, respiratory and esophageal abnormalities, cystic fibrosis, other malformations or non-specific anomalies, and HIV infection) a propensity score using the inverse probability of treatment weighting (IPTW) method will be used to reduce potential indication bias from abrysvo versus nirsevimab immunization. First, the probability of receiving abrysvo or nirsevimab will be estimated for each child using a logistic regression model based on all baseline covariates. These probabilities will be used as propensity scores, and weights will be calculated using the IPTW ATE approach. In the main and subgroup analyses, the comparative effectiveness of abrysvo and nirsevimab against hospitalization for RSV-related LRTI will be estimated using a logistic regression model, based on the propensity score detailed above. For all models, comparative effectiveness will be calculated as 100*(1 – OR), OR being the odds ratio reflecting the association between immunization and study outcomes.