 On a random basis, patients will receive one of the rPA formulations. Two doses of rPA will be evaluated, 10 microgram Microg and 20 Microg. This evaluation aims to establish the safety and most desirable level of dosage. Patients will receive one injection of the vaccine, administered in the left shoulder or left thigh. About 30 minutes later, their temperature will be taken, and the injection site will be inspected. Rare but severe reactions could occur if there is extreme sensitivity to a vaccine. However, such an occurrence is extremely rare following a vaccine, and if there are any dangerous symptoms, they can be effectively treated by medications available to patients while they are at the clinic. If there are no significant abnormal results, patients may return home. About 6 hours later and daily for 7 days, they will take their temperature and examine the injection site. The vaccine may cause temporary discomfort at the site of injection, and participants may experience a mild fever for 1 or 2 days after vaccination. 