In contrast, NAB levels equivalent to 30610 reciprocal dilution were detected in naïve animals given the PEGylated vaccine ( Figure 6B ). Samples obtained from animals given the unmodified virus had levels of 2065 reciprocal dilution. Animals with preexisting immunity against adenovirus and treated with the PEGylated preparation were also able to produce detectable levels of NAB (1065 reciprocal dilution) whereas NAB was not found in sera from mice given the unmodified vector orally. Further characterization of Ebola glycoprotein-specific Ig isotypes revealed that the PEGylated vector could possibly stimulate production of IgG in the presence or absence of pre-existing immunity with respect to levels found in animals given the unmodified vector ( Figure 6C ). Modification of the virus induced a slight increase of IgA in the presence of pre-existing immunity with respect to that seen in naïve animals given unmodified virus (Vaccine, Figure 6D ) and those with pre-existing immunity (Vaccine+PEI). Despite this, animals with pre-existing immunity to adenovirus and immunized with the PEGylated vaccine orally did not survive after challenge with 200 LD 50 of (MA)-ZEBOV.