<qa>  What is the dose of the E.coli derived rPA vaccine administered by intramusThis study will provide preliminary safety and comparative immunogenicity data for the E.coli derived rPA vaccine administered by intramuscular IM injection at Day 0 and Month 1.Doses will range from 5 μg to 100 μg rPA, and at each dose-level, rPA will either be combined with phosphate-buffered saline PBS or adsorbed to Alhydrogel. 