Adherence to the nirsevimab immunization campaign: analysis of sociodemographic and medico-economic influences-single-centre prospective cohort study in France.

Respiratory syncytial virus (RSV) is a common and highly contagious viral pathogen responsible for acute lower respiratory tract infection in infants. It represents an important public health and economic concern. This study, performed in a level 3 perinatal center, evaluated adherence to the first French national RSV immunization campaign with nirsevimab. This retrospective single-center study included 1361 newborns born at 34 weeks of gestation or after, from October 1, 2023, to January 10, 2024 in France. Data collected included sociodemographic and medico-economic characteristics of families (parents and newborns), and nirsevimab administration. Multivariable logistic regression was performed to determine factors associated with immunization acceptance. Overall, 87.7% of newborns received nirsevimab. The median postnatal age at administration was 2.8 days. Among parents initially refusing the administration, 17.7% of their infants (12/68) finally received the product, and among those initially reluctant to its administration, 57.4% (101/176) of their infants received it. On multivariable analysis, maternal birth in France, mother's occupation, and adherence to recommended vaccination during pregnancy were positively associated with passive immunization acceptance; delivery in January was negatively associated. CONLUSION: The study observed a high adherence rate to the 2023-2024 RSV immunization campaign. The administration of nirsevimab free of charge and before maternity unit discharge may have contributed to these results. Socio-demographic and medico-economic factors appeared to influence immunization adherence, suggesting that the period before maternity hospital discharge could represent a key time to carry out preventive actions and reduce social and territorial health inequalities. WHAT IS KNOWN: • Respiratory syncytial virus (RSV) is among the leading causes of acute lower respiratory-tract infection in young children with substantial economic impacts. • The first national passive immunization campaign against RSV was launched during the 2023-2024 RSV epidemics in France. WHAT IS NEW: • Medical, social, and territorial factors associated with parental adherence to passive immunization for their newborns are unknown. • Despite high adherence rates, disparities in passive immunization with nirsevimab uptake underscore the need for targeted interventions to ensure equitable access to healthcare: differences in uptake, despite free access, highlight the need for targeted communication and support strategies to overcome non-financial barriers and ensure equitable preventive care.