Participants will be assigned to groups, as well as, product randomly. For instance, the first study participant could be enrolled into group 3. The Dryvax® (Registered Trademark) dose is given as a challenge to see if the person has a take. A reduced take response or no take, could suggest that MVA is able to produce an immune response. The dosing schedules vary from 12 to 24 weeks and volunteers are in the study a total of 24 to 36 weeks, depending on the number of injections.