Figure 3. Protection by mucosal intranasal immunization in BALB/c mice. Groups of 5 female BALB/c mice were immunized intranasally with 10-fold serial dilutions of Ad4 or Ad7 expressing the centralized HA1-con hemagglutinin gene. Three weeks after immunization the mice were challenged with 100 MLD₅₀ of mouse-adapted influenza A/PR/8/34. Protection against weight loss and survival induced by the Ad4 vaccine is shown in A and B, respectively. Protection against weight loss and survival induced by the Ad7 vaccine is shown in C and D, respectively. Mice that lost 25% of baseline body weight were humanely euthanized.