The most direct means of evaluating vaccine efficacy in mice is to assess protection by monitoring weight loss and death rates after a lethal challenge of Ebola [43] . Therefore, mice were immunized with 1610 10 pre-existing immunity. At the time of vaccination, animals had an average anti-adenovirus neutralizing antibody titer of 1:320 reciprocal dilution. Naïve mice vaccinated by intramuscular injection with saline (vehicle) served as controls for complete lethality following challenge with mouse-adapted Ebola virus. Twenty-eight days after vaccination, animals were challenged with 200 LD 50 of mouse-adapted (MA)-ZEBOV. Only mice immunized by the nasal route survived the lethal challenge ( Figure 5A ). This was evident as early as 5 days after challenge when controls and mice immunized by the other routes began to lose weight ( Figure 5B ). All eventually expired 7 days post-challenge ( Figure 5A , some data not shown for clarity). In contrast, naïve mice given the vaccine survived challenge regardless of the route of administration.