No consistent evidence of decreased exposure to varicella-zoster virus among older adults in countries with universal varicella vaccination.

Abstract

BACKGROUND\nUniversal varicella vaccination might reduce opportunities for varicella-zoster virus (VZV) exposure and protective immunological boosting, thus increasing herpes zoster incidence in latently infected adults. Here, we assessed humoral and cell-mediated immunity (CMI), as markers of VZV exposure, from adults aged ≥50 years.\n\n\nMETHODS\nWe repurposed data from placebo recipients in a large multinational clinical trial (ZOE-50, NCT01165177). Countries were clustered based on their varicella vaccination programme characteristics, as having high, moderate or low VZV circulation. Anti-VZV antibody geometric mean concentrations, median frequencies of VZV-specific CD4 T cells and percentages of individuals with increases in VZV-specific CD4 T cell frequencies were compared across countries and clusters. Sensitivity analyses using a variable number of timepoints and different thresholds were also performed for CMI data.\n\n\nRESULTS\nVZV-specific humoral immunity from 17 countries (12 high, two moderate, three low circulation) varied significantly between countries (p<0·0001) but not by VZV circulation. No significant differences were identified in VZV-specific CMI between participants from two high versus one low circulation countries. In 3/5 sensitivity analyses, increases in CMI were more frequent in high VZV circulation countries (0.03≤p<0.05).\n\n\nCONCLUSIONS\nWe found no consistent evidence of reduced VZV exposure among older adults in countries with universal varicella vaccination.