Fig. 2.

Linear regression analysis of the relationship between Env divergence from vaccine strain and protection from EIA. The percentage of animals protected from disease in each trial group was plotted as a function of the level of amino acid divergence of the challenge strain envelope from the vaccine strain envelope. Linear regression (gray line) analysis (GraphPad Prism v. 4.0) revealed a direct, significant inverse linear relationship between the two variables, with an r² value of 0.99 (P = 0.02). Hence, “X” is predictive of “Y,” or divergence away from the Env of the vaccine strain is predictive of protection from disease.