FDA AGREES TO ANIMAL RULE FOR SOME VACCINES. “One challenge … bioweapon threats is the absence of some of these disease agents in the natural world. Vaccine efficacy is more difficult to establish when natural exposure to a pathogen is impossible … and when human challenge studies are not feasible. The FDA accepts animal testing for proof of efficacy in these cases.”
http://www.historyofvaccines.org/content/articles/biological-weapons-bioterrorism-and-vaccines