Dose Safety, Tolerability, and Immunogenicity of a New Smallpox Vaccine in Adults Without Previous Smallpox Vaccination

In addition to assessment of safety parameters, the objective of this study is to determine the minimum dose of ACAM1000 that is calculated to produce a major cutaneous reaction in at least 90% of a population of healthy adults 18-29 years of age and naïve to smallpox vaccine. Specifically, the objectives of this study are to: 1. Compare the safety and tolerability of three dose levels of ACAM1000 and a standard dose of Dryvax® in healthy adults 18-29 years of age and naïve to smallpox vaccine. Safety and tolerability will be determined by examination of the local cutaneous reaction, adverse events, physical examinations, vital signs, structured interviews, and laboratory analysis. 2. Determine the immunogenicity of three dose levels of ACAM1000 and a standard dose of Dryvax® in healthy adults 18-29 years of age by comparing: (a)the proportion of subjects at each dose level who develop a major cutaneous reaction; (b)the proportion of subjects in each treatment group who develop neutralizing antibodies, including the fold-increase in antibody titer between Baseline and Day 30 sera; and the geometric mean vaccinia neutralizing antibody titer on Day 30. 3. Determine the minimum dose of ACAM1000 that is calculated to produce a major cutaneous reaction in at least 90% of a population of healthy adults 18-29 years of age and naïve to smallpox vaccine.