Maternal Immunization Against Respiratory Syncytial Virus: An Updated WAidid Consensus Document on Evidence, Implementation, and Public Health Priorities

Background: Respiratory syncytial virus (RSV) is a leading cause of acute respiratory tract infec-tion and a major contributor to lower respiratory tract disease, hospitalization, and intensive care admission in young infants. The burden of severe disease is greatest during the first months of life, when active infant immunization is not yet feasible or may not provide sufficiently rapid protec-tion. The recent availability of prefusion F protein–based vaccines and long-acting monoclonal antibodies has transformed the RSV prevention landscape, making protection during early in-fancy an achievable public health objective. Methods: This consensus document summarizes and critically appraises updated evidence on RSV epidemiology, disease burden, seasonality, pre-ventive strategies, and implementation challenges, with a specific focus on maternal immuniza-tion. Evidence was reviewed in relation to infant protection, transplacental antibody transfer, optimal timing of vaccination during pregnancy, integration into antenatal care, and the posi-tioning of maternal vaccination alongside infant monoclonal antibody prophylaxis. Results: RSV imposes a substantial clinical and economic burden in infancy, including among previously healthy term infants, with the most severe outcomes concentrated in the first months after birth. Post-pandemic changes in RSV circulation have reduced the predictability of seasonal patterns, challenging prevention strategies based solely on traditional RSV seasons. Maternal RSV vac-cination provides passive protection to newborns through transplacental transfer of neutralizing antibodies and has demonstrated efficacy in reducing medically attended RSV-associated lower respiratory tract infection, severe disease, and hospitalization in early infancy. However, re-al-world effectiveness depends on several factors, including gestational age at vaccination, the interval between vaccination and delivery, prematurity, maternal immune response, vaccine uptake, and local RSV epidemiology. The coexistence of maternal vaccination and infant mono-clonal antibody prophylaxis requires clear, coordinated recommendations to prevent gaps in protection and support efficient resource allocation. Conclusions: Maternal immunization is a clinically relevant strategy to protect infants against RSV during their period of greatest vulner-ability. Successful implementation will require integration into routine antenatal care, adaptation to local epidemiology, coordination with monoclonal antibody programs, and continued sur-veillance of effectiveness, safety, uptake, and equity. A flexible prevention framework combining maternal vaccination and infant monoclonal antibody prophylaxis, according to local needs and individual risk, has the potential to substantially reduce RSV-associated morbidity, hospitaliza-tions, and healthcare burden in early infancy.