Clinical trials to assess the efficacy of vaccines against anthrax are not ethical or feasible, but data from 21 US government–sponsored animal studies on anthrax vaccine efficacy indicate that an in vitro anthrax lethal toxin neutralization activity assay (TNA), which measures how well antibodies in the blood can block anthrax toxin, can predict survival against an inhalation anthrax challenge within and across species and genera (Fay MP et al. Sci Transl Med. 2012;4:151ra126).
Hampton T. Anthrax Vaccine Testing. JAMA. 2012;308(17):1729. doi:10.1001/jama.2012.28156