Use of the FDA Animal Rule for licensure of Ebola and Marburg virus vaccines requires a detailed understanding of vaccine-induced immune response since correlates of immunity will replace efficacy studies that would otherwise be provided to support vaccine licensure. An immune correlate of protection against infection must first be identified in an animal model that reasonably represents disease pathogenesis in humans. Vaccine efficacy is tested in animals, and the immune response that correlates best with survival is identified. Subsequent immunogenicity studies in human subjects are designed to test whether the vaccine can induce similar responses in humans.