Fig 6. Morbidity and survival following challenge in young and elderly mice.

(A-D) Groups of BALB/cAnNCr mice or (E-H) BALB/cJ mice were immunized to A/NP+M2 (N = 6 to 8) or B/NP (N = 6 to 7) by DNA priming followed by rAd boosting. They were challenged with 200 TCID₅₀ of A/FM-ma one month after rAd. (A, C, E, and G) Weight loss after challenge shown as the mean + SD. (B, D, F, and H) Survival until weight loss endpoint after challenge. Animals were euthanized if weight decreased by more than 30% of the individual starting weight (a pre-determined endpoint for this experiment so that even weak protection would have been seen in 20-month-old mice, if present). Not all groups were vaccinated and challenged simultaneously, but each old group was vaccinated and challenged simultaneously with a young control group of the same BALB/c subline. Young animals in different groups showed similar results.