For unique circumstances, such as those where conventional efficacy trials are not feasible, the U.S. Food and Drug Administration has created the “animal rule,” which states that licensure can be approved on the basis of animal model studies that replicate human disease combined with safety and immunologic data from humans (4). Nonhuman primates serve as the gold standard for animal models of Ebola infection and have been used to test Ebola vaccine candidates, with promising results (Table). Alternate vaccine candidates have specific properties that must be taken into consideration for selection of the ideal vaccine under given circumstances. For example, one that requires several weeks to develop immunogenicity, such as the recombinant adenovirus–based DNA vaccine, could be appropriate in high-risk settings not currently affected by an Ebola outbreak (2). Similarly, a vaccine that remains viable at ambient temperatures, such as the Ebola subunit vaccine (5), could be stockpiled as part of a preparedness strategy. In contrast, the species-specific properties of a recombinant cytomegalovirus vaccine make it a candidate for wildlife vaccination in Ebola-endemic areas (6). Although a wildlife vaccination strategy would not be the focus of a containment strategy to control an outbreak already in a human population, it may be a component of a longer-term strategy to reduce Ebola zoonosis. With regard to the current outbreak, given that the rVSV vaccine has shown efficacy in eliciting both prophylactic and postexposure protection (3), it is probably the vaccine of choice for persons in a high-risk setting who may have already been exposed. The rVSV vaccine has also been found to be effective in primates infected with simian immunodeficiency virus (7) and may therefore be particularly well-suited for use in populations with a high prevalence of HIV. We believe that the safety risks of vaccines, particularly those found to be safe in phase 1 clinical trials, are probably negligible compared with the risks faced by health care workers in communities where the highly virulent Ebola virus is currently circulating.