Optimal Immunization Strategy for Protection of Children < 1 Year Against Respiratory Syncytial Virus Infection and...

Respiratory Syncytial Virus (RSV) can lead to severe bronchiolitis and pneumonia, especially in children under one year of age. The introduction of vaccines and immunoprophylaxis has highlighted the need for more representative models to evaluate their impact on public health strategies. In Spain, Nirsevimab, a recombinant human monoclonal antibody against RSV, was added to the 2023 immunization schedule for children, administered as a single intramuscular dose. We developed an agent-based model representing the population of the Valencian Community (CVA), Spain, to simulate RSV transmission and assess various immunization strategies. This model integrates demographic factors and incorporates random transitions between states. It also takes into account that the effectiveness of existing immunoprophylaxis decreases over time. Using this model, we systematically evaluated 133 contiguous-month immunization strategies and the non-immunization scenario. To determine the effectiveness of these strategies, we compared simulated outcomes related to hospitalizations in children aged 0-5 months and those under one year, as well as the incidence of infections in these age groups. Our findings show that several immunization strategies effectively reduce hospitalizations and infections in infants aged 0-5 months to a similar extent. Targeting newborns between October and March/April, along with immunizing children under one year of age born outside this period in October, consistently ranks among the best-performing approaches across multiple evaluation criteria. These strategies offer a strong balance between health impact and immunization effort, and are particularly effective in reducing hospitalizations among infants under one year.