Figure 2. Results of matrix protein 2 (M2)e–keyhole limpet hemocyanin (KLH) vaccination, showing cross-protection. Mice (7–9 per group) were vaccinated as in Figure 1. Six weeks after the booster, they were anesthetized with isoflurane and challenged with 10x the 50% lethal dose (LD50). Of A/PR/8 (A) or A/FM (B) viruses and then monitored for survival. Cumulative survival rates after challenge with A/PR/8 or A/FM virus differed significantly from those of KLH controls for all M2e-conjugates (p = 0.001 and p<0.001, respectively, log-rank). e, ectodomain.