The Shingles Prevention Study demonstrated that high potency live attenuated Oka/Merck varicella-zoster virus (VZV) vaccine reduced the Burden of Illness (BOI) due to Herpes Zoster (HZ) by 61%, reduced the Incidence of Postherpetic Neuralgia (PHN) by 67%, and reduced the incidence of HZ by 51%. This large, prospective, placebo-controlled trial in which 38,546 subjects were stratified into two age group (60-69 and ≥70) provided an opportunity to examine the impact of age on the clinical manifestations of HZ; on VZV-specific immune responses at baseline, following zoster vaccine and following HZ; and on vaccine efficacy.

Data from placebo recipients confirmed an increase in incidence and severity of HZ in older persons. The increased incidence in =70 year olds compared with 60-69 year olds was less than 10%, but the HZ BOI, a measure of total HZ-associated pain and discomfort, was nearly twice as great in the older age group, reflecting a marked increase in disease severity. Also reflecting this increase in severity, the incidence of PHN was almost three-fold greater in the older age group. The Study confirmed the age-related decline in baseline levels of CMI to VZV and demonstrated an age-related reduction in CMI responses to zoster vaccine and to HZ. Because it markedly reduced disease severity, vaccine efficacy for HZ BOI and for PHN were well maintained in the older age group, despite a reduced effect on the incidence of HZ.