Genes of highly conserved proteins such as the nucleoprotein or M2 proteins could be included in adenovirus vector-based vaccines because immune responses against these infl uenza viral antigens provide protection in animal models (24, 25) . Recently, human adenoviral vector-based HA subtype 5 infl uenza vaccine induced protection in mice against infl uenza (H5N1) viruses isolated from humans (26, 27) . However, pre-existing immune response to human adenoviruses could be a potential problem in the generation of immune response against a foreign gene of interest. Delivering the vaccine nasally could largely overcome this problem because there appears to be no pre-existing immunity in the upper airways. Moreover, a robust CD8 T-cell response would likely be fl exible and able to fi ght infl uenza (H5N1).