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 1000 LD50 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 with the Vollum 1B strain than with the Ames strain, although vaccine efficacy against the Ames strain was better than previously reported. Enzyme-linked immunosorbent assay of serum antibody titres to B. anthracis protective antigen showed that there was no significant correlation between survival and antibody titres.