Frequency of glycoprotein E (gE)–specific CD4 T cells expressing any combination of activation markers (according-to-protocol cohort for immunogenicity). A, Mean gE-specific CD4 T-cell frequencies. B, Relative mean gE-specific CD4 T-cell frequencies. C, Activation marker combinations (error bars represent interquartile ranges). Abbreviations: CD40L, CD40 ligand; HZ-NonVac, no previous vaccination with live-attenuated herpes zoster (HZ) vaccine before administration of adjuvanted recombinant zoster vaccine (RZV); HZ-PreVac, previous vaccination with live-attenuated HZ vaccine ≥5 years before administration of adjuvanted RZV; IFN-γ, interferon γ; IL-2, interleukin 2; mo, month(s); TNF-α, tumor necrosis factor α.