Together the data suggests that PAV3 vector is an additional option to AdHu5 vector and could have several important applications including rapid or post-exposure protection against emerging influenza viruses or other infectious agents. A similar study described a BAV3-HA vaccine sharing comparable protective efficacy to the AdHu5-HA against an H5N1 virus. Two doses of the BAV3 vector generated similar humoral and cellmediated immune responses and was able to evade pre-existing neutralizing antibodies against AdHu5 [12] . Overall protective efficacy offered by PAV3-HA was similar to AdHu5-HA one month post-immunization and the immune response kinetics was also generally comparable at later time points. Although not explored in the current study, previous studies have evaluated the impact of pre-existing immunity to PAV3 and the potential reuse of PAV3-based vectors against different pathogens. Groups of outbred pigs with high PAV3 neutralizing antibody titres were vaccinated with a PAV3-based vaccine and vector re-administration did not result in hepatotoxicity or reduced transgene expression [14] . Doses of 10 13 particles/kg AdHu5 vector can also bypass pre-existing immunity, however, several pathologies including liver damage indicated by elevated transaminase, low platelets count, and lymphocytopenia were observed in nonhuman primates administered similar doses [9, 10, 34, 35] .