Gut Microbiome and Immune Response in Severe RSV Infection in Vietnamese Infants

This is a single-center, prospective observational study conducted at Vietnam National Children's Hospital in Hanoi over 48 months. Approximately 250 infants aged 1-24 months with RT-PCR-confirmed RSV lower respiratory tract infection will be enrolled and classified into severe vs mild groups based on need for advanced respiratory support (HFNC/CPAP/invasive ventilation) and/or PICU admission versus no/low-flow oxygen requirement. Stool samples collected within the first 24 hours of admission will undergo 16S rRNA sequencing (V3-V4 region) to characterize gut microbiome diversity and taxa abundance. Blood samples collected within the first 24 hours will be used to quantify key cytokines (e.g., TNF-α, IL-6, IL-8, IL-1β, IFN-γ, IL-10, IL-17A, IL-22) using ELISA; immune cell subsets may be assessed by flow cytometry. Clinical severity will be assessed using standardized pediatric scores (PRISM III, PELOD, pSOFA) and treatment outcomes will be recorded. The study will evaluate associations among microbiome features, immune response markers, and RSV severity to propose candidate integrated biomarkers for early risk stratification.