<qa>  What is the primary efficacy endpoint for this trial?The purposes of this multi-center, double blind randomized dose response study are: to evaluate the safety of undiluted Dryvax and Dryvax diluted at 1:5 and 1:10 in adults between the ages of 32 and 70 years who were previously vaccinated but not since 1989 and to define, with very high precision -3, the proportion of individuals who respond with a take 6 to 11 days after vaccination with undiluted Dryvax vaccine and Dryvax diluted at 1:5. A take is defined as the formation of a lesion at the site of vaccination that is consistent with the description of a successful vaccination described in the IB Secondary study objectives include defining with good precision - 10, the proportion of individuals who respond with a take 6 to 11 days after vaccination with a 1:10 dilution of Dryvax vaccine and exploring correlations between takes no-take and immune responses in all vaccine groups antibody responses in all volunteers; and assays of cell-mediated immunity in a convenience sample consisting of 15 volunteers enrolled at each site total N 105 randomly distributed across the vaccine groups. Immunogenicity assays will include neutralizing antibody to vaccinia, vaccinia binding antibody, ELISPOT for gamma interferon Assays of cell-mediated immunity will be performed only on a convenience sample consisting of 15 volunteers enrolled at each site total N 105 and intracellular cytokine production. Primary safety endpoints include safety data regarding the three doses of vaccine in previously vaccinated subjects as assessed by adverse events reported by the subjects andor investigators and changes observed during the scheduled clinic visits. Specific attention will be paid to the following: local reactogenicity at the site of injection: pain, tenderness, erythema, induration, regional lymphadenopathy, limitation of limb movement; systemic symptoms: fever, myalgia, fatigue, and headache; anaphylaxis, and hypersensitivity reactions; other reactions: dermatologic, neurologic, gastrointestinal nauseavomiting, diarrhea. The primary efficacy endpoint for this trial will be the proportion of vaccinees demonstrating a take 6 to 11 days after the first vaccination at each of the dose levels undiluted and 1:5 and 1:10. Secondary endpoints are: immune responses as assessed by vaccinia neutralizing antibody measured on all subjects and binding antibody to vaccinia on all subjects and the size of the lesions observed in all subjects compared across the dilution groups. Tertiary endpoints of 15 volunteers at each site randomly distributed across the vaccine groups are cellular immune responses as assessed by: ELISPOT for gamma interferon in response to vaccinia antigens and intracellular cytokine production. 