Bolanos, RafaelAraos Bralic, Rafael IgnacioGonzalez, CeciliaSepulveda, DinoFalconi, JuanAverin, AhuvaAtwood, MarkQuinn, ErinLaw, AmyMendes, Diana2026-09-022026-09-022025Bolanos R, Araos R, Gonzalez C, Sepulveda D, Falconi JF, Averin A, Atwood M, Quinn E, Law AW, Mendes D. Cost-effectiveness of strategies using preventive interventions to protect infants in Chile from respiratory syncytial virus. Expert Rev Vaccines. 2025 Dec;24(1):904-913. doi: 10.1080/14760584.2025.2562201https://hdl.handle.net/11447/11056Background: Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract illness (LRTI; RSV-LRTI) among infants in Chile; young infants and infants born prematurely are at greatest risk. Research design and methods: A cohort model was developed to evaluate cost-effectiveness of strategies preventing RSV-LRTI in infants. Using the model, we calculated the economically justifiable price (EJP) of maternal RSVpreF vaccination (MV) versus no intervention and then evaluated the cost-effectiveness of MV (cost/dose assumed at EJP) with complementary use of monoclonal antibody nirsevimab for unprotected infants (MV+N) versus nirsevimab alone (NA) to prevent RSV-LRTI. Nirsevimab published price was $260.00; costs/prices reported in 2023 US$. Results: NA yielded 20,247 cases (hospital: 3,773, emergency ward: 16,474) and $57.2 million (M) in total costs (medical: $6.3 M, intervention: $48.7 M, indirect: $2.2 M). MV+N yielded 23,906 cases (hospital: 3,137, emergency ward: 20,769) and $28.7 M in costs (medical: $4.8 M, intervention: $21.7 M [RSVpreF assumed $75.77/dose; nirsevimab procured $260.00/dose], indirect: $2.2 M). With costs lower by $28.4 M and increased quality-adjusted life-years, MV+N would be cost-saving versus NA. Conclusions: RSVpreF vaccination among pregnant women along with nirsevimab for unprotected infants in Chile would be the most efficient use of resources, yielding substantial cost savings compared to use of nirsevimab alone. Trial registration: ClinicalTrials.gov NCT04424316 NCT03979313.enChileRespiratory syncytial virusesCost-effectiveness analysisInfantsMonoclonal antibodiesVaccineArticlehttps://doi.org/10.1080/14760584.2025.2562201