Bacillus anthracis is a gram-positive, spore-forming bacteria that causes anthrax infection in humans. CDC inventors have identified epitope sequences of B. anthracis protective antigen (PA) that may be useful for development of peptide-based anthrax vaccines. This invention also relates to methods for determining whether post-vaccination protection is achieved. Specifically, this invention relates to a screening method for determining protection against B. anthracis infection that involves testing a biological sample for the presence of antibodies to one or more predefined regions of B. anthracis PA. This technology may be important to any bioterrorism defense strategy.