(The statistical methods to examine this hypothesis require computing the relative risk, and corresponding 90% confidence interval, of confirmed hepatitis A disease among those receiving vaccine compared to those receiving IG, within 14 days of exposure. Inference of similarity involves examining the upper bound of this confidence interval and translating this RR bound into a lower bound of the 90% confidence interval for vaccine efficacy. Translation from relative risk to efficacy depends on an assumption of the point estimate of the efficacy of IG, based on historical data, the particular design of this study and assumptions regarding how transmission of hepatitis A virus occurred in the study population.) Study Design and Duration: Randomized, double-blinded, comparative, experimental epidemiologic study. Study will be conducted among exposed contacts 2-40 years of age in the household exposure group and is expected to last 18 months.