Hypotheses and Specific Aims The investigators will test the hypotheses that VAS at birth will (1) improve production of new T cells at 1-2 yr of age; (2) improve T-cell memory responses at 1-2 yr of age to vaccines given early in infancy (birth - 14 wk); and (3) alter intestinal colonization early in infancy (6, 11 and 15 wk) and at 1-2 yr of age to increase Bifidobacterium and other healthy bacteria and decrease Proteobacteria and other harmful bacteria. Because the "secretor status" of the mother affects the carbohydrate content of the breastmilk, which can in turn affect Bifidobacterium growth in the infant gut, the "secretor status" of the mother will be determined. Furthermore these differences in composition of the intestinal bacteria will be associated with greater immunologic responses to oral and systemic vaccines.