Figure 7: Live virus challenges with A/Philippines/82 and A/Puerto Rico/8/34 strains. Immunized mice were challenged with a lethal dose (5LD50) of A/Philippines/82 or A/Puerto Rico/8/34 in a volume of 30 μL PBS by i.n. instillation. Each group has 3 mice. Mouse survival rate and body weight changes were monitored daily for 14 days. Each group has 3 mice. Mouse lung virus titers at day 4 postchallenge were determined by a standard plaque assay. Each lung sample was grinded, cleared, and diluted in 2ml DMEM. Bars represent mean virus titers (Log10 pfu/mL) ± standard errors from three independent assays. The asterisk (*) indicates a significant difference between group immunized with stM2e only and other groups, (*). (a) and (b) Lung virus titers at day 4 and survival rate after A/Phi/82 virus infection; (c) and (d) lung virus titers at day 4 and survival rate after PR/8 infection.