Assessment of the Immunogenicity and Safety of a Dose-Sparing BioThrax® AVA Schedule

This is a Phase IV, randomized, open-label immunogenicity and safety study to evaluate four dosing regimens of BioThrax® for Post-Exposure Prophylaxis (PEP) for anthrax. BioThrax® will be administered as a subcutaneous (SC) injection for the primary series and will be administered as an intramuscular (IM) injection for the boost. The four dosing regimens are: 0.50mL BioThrax® on Days 0, 14, and 6 month boost; 0.50mL BioThrax® on Days 0, 28 and 6 month boost; 0.50mL BioThrax® on Days 0, 14, 28 and 6 month boost and 0.25mL BioThrax® on Days 0, 14, and 28, 6 month boost with 0.50ml IM Approximately 300 subjects will be randomized 1:1:1:1 to one of the four study arms. Enrollment will be stratified by gender, with approximately equal numbers of males and females (18 through 65 years) enrolled into each dosing regimen. The Primary objective is to evaluate the immunogenicity of the four dosing regimens of BioThrax® using the Toxin Neutralization Assay (TNA). The secondary objective is to evaluate the safety of the four dosing regimens of BioThrax®.