Although the frequencies of specific effector memory CD4+ T-cells and effector CD4+ T-cells after vaccination were approximately double and half, respectively, of those after infection, these differences were not significant (Figure 2B) (mean Tem 0.189% ± 0.049 versus 0.090% ± 0.035 and mean Teff 0.006% ± 0.002 versus 0.010% ± 0.003, respectively). Here, CD4 is linked to infection.