Maternal RSV immunization: clinical efficacy, immunological mechanisms and public health implications for preventing infant lower respiratory tract infection.

Respiratory syncytial virus (RSV) remains a leading cause of infant morbidity and mortality, with the highest burden concentrated in low- and middle-income countries (LMICs). Existing preventive options, including long-acting monoclonal antibodies, can be constrained by cost, logistics, and access, leaving many high-risk infants unprotected. This article is a structured narrative review summarizing clinical efficacy, immunological mechanisms, safety and public health implications of maternal RSV immunization for preventing infant RSV lower respiratory tract infection (LRTI), with an explicit implementation focus for LMICs. Evidence was identified through targeted searches of major biomedical databases and prioritized by clinical relevance and policy importance, including phase III efficacy trials, regulatory and technical documents, post-authorization safety signals, and modelling studies evaluating potential impact in LMICs. Across the evidence base, maternal vaccination induces robust RSV-neutralizing IgG responses and efficient transplacental antibody transfer, providing passive protection during the first months of life when RSV risk is highest. In phase III data, maternal RSV vaccination demonstrated high efficacy against severe medically attended RSV LRTI in early infancy (e.g., up to 81.8% within the first 90 days for a licensed maternal RSV vaccine). Modelling studies project substantial global reductions in hospitalizations and deaths, although real-world effectiveness in LMICs will depend on antenatal care coverage, timing feasibility, seasonality, and equity of delivery. Safety findings were generally favorable; nonetheless, continued post-licensure monitoring,particularly for pregnancy and birth outcomes such as preterm birth,remains essential. Maternal RSV immunization is a scalable strategy that can leverage existing antenatal platforms and, if equitably implemented, could meaningfully reduce infant RSV morbidity and mortality, especially in LMIC settings.