Although no immunologic correlate o

Although no immunologic correlate of protection against herpes zoster has been identified,CD4+ and CD8+ T cells are believed to play a central role in preventing VZV reactivation.14,26-29 In our study, the observation that vaccine effi- cacy was maintained even among patients in the oldest age group, in conjunction with previous clinical data showing that HZ/su immunogenic- ity decreases only minimally with increasing age, suggests that HZ/su can overcome immunose- nescence to provide protection against herpes zoster.19,21,30-32 The immune response to HZ/su in both older persons and those with immuno- suppression that was observed in earlier clinical studies might be attributed to the AS01B adjuvant system, which boosts VZV-specific memory im- mune responses.20,33 Glycoprotein E adjuvanted with AS01B elicits higher glycoprotein-E–specific CD4+ T-cell and humoral immune responses than does unadjuvanted glycoprotein E, glycopro- tein E adjuvanted with alum, or glycoprotein E adjuvanted with AS01 formulations containing lower amounts of the MPL and QS21 immuno- stimulants.18,20,21 Therefore, although the small number of HZ/su recipients with herpes zoster
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in our study may prove insufficient to define an immunologic correlate of protection, future analyses of HZ/su immunogenicity will be of interest in explaining how an immune response targeting a single VZV antigen provides age- independent protection against herpes zoster in older adults.