Major depressive disorder and immunity to varicella-zoster virus in the elderly

► Lower levels of varicella-zoster virus cell-mediated immunity (VZV-CMI) explain the increased risk and severity of herpes zoster. ► Increasing age lowers VZV-CMI and is associated with increased risk of herpes zoster. ► The occurrence of major depression in older adults further lowers VZV-CMI. ► Severity of depressive symptoms, along with increasing age, correlate with lower levels of VZV-CMI in depressed subjects. ► Depression, and its severity, may add to the risk of herpes zoster in older adults.