Kaplan-Meier survival curves for the mice (eight mice per group) vaccinated with pE3-E2-6K-E1, p6K-E1, or pE3-E2 and challenged with a lethal dose of a heterologous strain of WEEV. The vaccinated mice were challenged intranasally with low-virulence strain CBA87 or high-virulence strain Fleming and were monitored for 14 days. The log rank test was used to assess the differences in the survival rates of the challenged mice. *, P < 0.01 for pVHX-6 versus pVAX; **, P < 0.01 for pE3-E2-6K-E1 versus pVAX; ***, P < 0.01 for p6K-E1 versus pVAX; #, P < 0.01 for pVHX-6 versus pVAX; ##, P < 0.01 for pE3-E2-6K-E1 versus pVAX.