 This is phase I, double blind, placebo-controlled safety and infectivity study of experimental human Norovirus genogroup GII.4 administered to healthy adults 18-49 years of age. Subjects susceptible to the human norovirus GII.4 challenge strain. The challenge study will be conducted in 2-3 cohorts of approximately 20 subjects each.Subjects will remain in the inpatient facility for at least four days following challenge and assessed daily for clinical and virologic evidence of norovirus infection. The primary objectives are to evaluate the safety and reactogenicity of the norovirus GII.4 CIN-1; 031693 challenge stock and to determine a safe and optimal challenge dose of Norovirus GII.4 Challenge Stock norovirus to achieve illness in 50 of subjects. Illness is defined as: diarrhea 3 loose or liquid stools or 300 gm of loose or liquid stool 24h, andor vomiting during the inpatient period, in a participant with evidence of infection. 