Fig. 2.
Sw/Iowa/30 vaccine provides protection against lethal challenge with a recombinant influenza virus possessing five 1918 virus genes. Groups of BALB/c mice were vaccinated as described in the legend of Fig. 1. Twenty-two days after vaccination, mice were challenged i.n. with 100 LD50 of 1918 HA/NA/M/NS/NP:WSN recombinant virus. Mice were monitored for survival (A) or killed 5 days later, and virus titers in individual lung, nose, and brain tissue were determined (B). An asterisk indicates that the H1N1-vaccinated group was significantly (P < 0.05) different from the control groups by ANOVA.