Although previous anthrax countermeasures were tested in the rabbit model, lower expression of Toll-Like Receptor 9 in the rabbit diminishes the potentiation provided by the adjuvant, meaning the rabbit has no predictive value for CpG adjuvanted vaccines.11 In contrast, the guinea pig model described herein has been shown to accurately predict the efficacy of CpG adjuvanted vaccines against anthrax.12 In this study, our results indicate that a single dose of AV7909 is less effective compared to the two-dose regimen in the guinea pig anthrax model. Here, TLR9 is linked to anthrax infection.