Study Plan: Part 1: 20 subjects will be enrolled, with 10 in each of the two dosage groups for cAd3-EBO. The dose escalation plan includes daily review of any new safety data by a study clinician, weekly review of safety data by the protocol team and a staged enrollment plan with required interim safety reviews before proceeding to the next step. The study plan includes no more than one enrollment per day for the first 3 vaccinated subjects in each group. After at least 3 days of follow-up, an interim safety review will occur before enrollment of additional subjects into the group. When there are at least 2 weeks of follow-up safety data for the first 3 vaccinated subjects in Group 1, an interim safety review will occur before proceeding to the next dose level.