Results of vaccination and booster with DNA prime–adenovirus (Ad), showing cross-protection. Mice (8–10 per group) were immunized as in Figure 4 or intranasally given a sublethal priming infection with A/PR/8. Three weeks later they were challenged with a high dose of A/PR/8 (1.5x 104 50% lethal dose [LD50]) or moderate dose of A/FM (10 LD50) and monitored for survival. The cumulative survival rate for mice immunized with A/PR/8 and M2-DNA+M2-Ad was significantly higher than that for mice immuni