Sample Size: Enrollment will continue until 44 hepatitis A cases in randomized subjects are observed. Assuming a 30% secondary attack rate in evaluable, confirmed contacts of index cases and a 90% efficacy rate of IG, to observe 44 laboratory-confirmed cases of hepatitis A, 1468 randomized subjects will need to be evaluable (734/group). Evaluable is defined as seronegative at baseline and with clinical follow-up data at Day 56. Assuming 90% of subjects have follow-up data and 45% of subjects are seronegative at baseline, 4067 subjects ages 2 to 40 years must be randomized (2038/group). The actual enrollment may be different based on validity of these assumptions.