Bivariate logistic regression analysis for association with (A) conservation, or (B) positive selection sites in S protein.

Coef: coefficient; Std. Err.: standard error; OR: odd ratio; CI: confidence interval; NS: not significant; na: not applicable. Logistic regression analysis was carried out with conservation as the predicted variable. (A) The estimated coefficients suggest that the conservation is significantly associated with structural region (α-helix+β-sheet) (Coef. = 0.64 with p = 0.041<0.5), but has no significant association with epitopes (Coef. = 0.49 with p = 0.058>0.05). This result is consistent with the results of Fisher’s exact test. (B) The logistic model with X1 and X2 as predictor variables is not significant due to the fact P(> χ2) >0.05.