ABSTRACT - CORE AND OPTIONAL COMPONENTS: Investigators at Seattle Children's Hospital propose to establish a site to conduct population-based surveillance for acute gastrointestinal and respiratory infections in children living in King County (population 1.9 million) seeking emergency care or requiring hospitalization for vaccine-preventable or potentially vaccine-preventable conditions. The New Vaccine Surveillance Network (NVSN) site in Seattle provides representation for the Pacific Northwest and the western USA within the national surveillance effort, capturing data from a geographic area with differences in rotavirus and respiratory viral seasonality as well as a state-based immunization program and varied vaccine acceptance rates. The Seattle researchers, led by Drs. Janet Englund and Eileen Klein, are experienced in surveillance for acute gastroenteritis (AGE), rotavirus disease, rotavirus vaccine-effectiveness (VE) studies, acute respiratory diseases, influenza vaccines, respiratory syncytial virus epidemiology, and studies in pregnant women, with a history of successfully conducting collaborative, innovative clinical studies of new and emerging pathogens, vaccines, and vaccine-preventable infections in diverse pediatric population. Seattle Children's Hospital, the only pediatric emergency department in the county, encompasses 85% of pediatric hospital beds, and provides acute care for ~85% of acute respiratory disease requiring hospital admission. We work closely with our state- wide immunization registry, which registers all children born in-state and over 96% of vaccines given to children, to assist in VE studies. With collaboration from the Public Health Department of Seattle-King County (PHSKC), we are able to collect admission data from all hospitals in King County and utilize county-wide surveillance programs tracking all emergency room admissions and hospitalization to calculate adjusted population-based disease and hospitalization rates. Our objectives will be to establish VE for rotavirus and influenza vaccines, calculate population-based disease and hospitalization rates, and detect new and re- emerging pathogens to inform public policy. We will assess the impact of new vaccines as they are developed and new vaccine policies as appropriate, and work collaboratively with other NVSN sites and the CDC to understand the burden of vaccine-preventable diseases by assisting the development of new, innovative projects and protocols. We will also recruit 200 pregnant women and follow these women and their infants for two years to assess enteric and respiratory diseases in mother-infant pairs, and household members, documenting the impact of maternal antibody and disease on childhood infection and severity of disease. We will add to the NVSN effort based on our history of enrollment of appropriate numbers of subjects and controls with documented vaccine histories, high levels of specimens collected which are analyzed at laboratories in Seattle and at CDC, and innovative studies proposed and conducted in high risk populations. The Seattle site will contribute to the understanding and documentation of specific pathogens and new vaccines in children.