Participants will be randomly assigned to one of two groups. Participants in Group 1 will receive tetanus toxoid immunizations (known as DTaP, DT-pediatric, or Td) at Weeks 8, 16, and 24 and hepatitis A vaccinations at Weeks 32, 40, and 48. Participants in Group 2 will receive hepatitis A vaccinations at Weeks 8, 16, and 24 and tetanus toxoid immunizations at Weeks 32, 40, and 48. Participants will have a physical exam and blood tests at study entry and at Weeks 4, 8, 12, 16, 24, 28, 32, 36, 40, 48, 52, 76, and 100.