Fig. 4.

Protection of immunized mice against a high-dose lethal challenge. At 4 weeks after immunization, mice were challenged by intranasal instillation of 100× LD₅₀ of mouse-adapted influenza virus A/PR/8/34. Mice were monitored daily after challenge and were killed when found to display severe signs of illness or loss of more than 25% body weight in accordance with Institutional Animal Care and Use Committee guidelines. Groups of 6 mice were immunized by MNs coated with 10 μg of BSA (control), MNs coated with 10 μg of IIV (MN), IM injection of 10 μg of IIV dissolved in PBS (IM), or IM injection of 10 μg of IIV dissolved in coating solution (CS). (A) Survival rate of each group of mice after challenge. (B) Percentage change of body weight in each group of mice after challenge.