Efficacy of a Standard Human Anthrax Vaccine Against Bacillus Anthracis Spore Challenge in Guinea Pigs

The efficacy of an anthrax vaccine licensed for human use, MDPH-PA, was tested in guinea pigs intramuscularly challenged with 10, 100 or 1,000 LD50s of spores from two virulent strains of Bacillus anthracis, Vollum 1B and Ames. As demonstrated in other investigations, immunization with MDPH-PA provided better protection against challenge from the Vollum 1B strain than from the Ames strain, although vaccine efficacy against the Ames strain was better than previously reported. Enzyme-linked immunosor bent assay of serum antibody titers to B. anthracis protective antigen showed no significant correlation between survival and antibody titer.