CD8+ T-cell responses induced by acute and chronic viral infections have different characteristics in terms of kinetics, response magnitude and T-cell specificity. Recently, American scientists Miller et al. performed a longitudinal analysis of CD8+ T-cell responses in smallpox and yellow fever vaccine recipients. Smallpox and yellow fever vaccinations mimic the course of acute viral infections well, with both vaccines eliciting a rapid production of large numbers of CD8+ effector T cells, peaking at about two weeks. When the primary response peaked, smallpox and yellow fever vaccine-specific CD8+ T cells accounted for 40% and 12.5% of CD8+ T cells in the blood, respectively. Functional analysis of tetrameric staining showed that virus-specific CD8+ T cells first exerted antiviral effects by expressing perforin and granzyme B. Immediately afterwards, the CD8+ effector T cell effect entered a contraction phase, where the number decreased to about 10% of the peak, and then gradually differentiated into CD8+ memory T cells capable of long-term survival, and the differentiation of effector T cells into memory T cells was continuous The process of differentiation of effector T cells into memory T cells is continuous.