Figure 1).

Cell-mediated immunity and development of herpes zoster (reproduced with permission from reference 1). Varicella is the primary infection caused by varicella-zoster virus (VZV), and its resolution is associated with the induction of VZV-specific memory T cells (blue line). Memory immunity to VZV may be boosted periodically by exposure to varicella or silent reactivation from latency (red peaks). VZV-specific memory T cell levels decline with age. The decline below a threshold (dashed green line) correlates with an increased risk of zoster. The occurrence of zoster, in turn, is associated with an increase in VZV-specific T cell levels. The administration of zoster vaccine to older persons may prevent VZV-specific T cell levels from dropping below the threshold for zoster occurrence (dashed blue line)