Previous studies have shown that PAV3 vectors can transduce several human cell lines resulting in full transgene expression and adenoviral coat proteins [20, 21] . An additional safety feature is that wild-type PAV3 does not replicate in human cells [21] , Groups of 6 BALB/c were vaccinated with 10 10 vp/mouse of PAV3-HA () or AdHu5-HA (), or no vaccine (Control, ()) and challenged with 100LD50 of H5N1-H05 on days 5, 8, and 10 post-vaccination. Lungs were harvested from the mice on day 3 post-challenge. Virus titre was determined by TCID50 assay using serial dilution of lung homogenates on MDCK cells and monitoring for the presence of CPE over 48 hours. The TCID50 titre was calculated by the Reed & Muench method [39] and normalized/gram of lung tissue. Data is presented as log 10 TCID50/g of lung tissue. The data represent average values and standard deviations from one experiment performed with one vector preparation of each vaccine (* and ** represents p,0.05). doi:10.1371/journal.pone.0015301.g004