Safety and immunogenicity of one or two additional doses of the adjuvanted recombinant zoster vaccine administered 5–6 years after primary vaccination in adults ≥50 years

Abstract Background A phase 3b extension of the ZOE-50/70 trials evaluated long-term efficacy, immunogenicity, and safety of the recombinant zoster vaccine (RZV) in participants ≥50 years, with a 6-year follow-up after completion of the primary studies. A subset of participants was evaluated for immunogenicity and safety of one or two additional doses administered 5–6 years after primary vaccination. Methods Participants were randomized to one additional dose (1-additional dose group, n=61), two additional doses (revaccination group, n=60), or no additional vaccination (control, n=119). Humoral and cell-mediated immunity were evaluated by anti-glycoprotein E (gE) antibodies, gE-specific CD4[2+] T-cells, and memory B-cells. Reactogenicity was evaluated for 7 days post-vaccination and overall safety was evaluated throughout the study. NCT02723773. Results Anti-gE geometric mean concentrations (GMCs) were 10,000–11,500 mIU/mL in all groups pre-additional vaccination. GMCs peaked at 1 month after one dose (73,834.4 and 79,419.8 mIU/mL in the 1-additional dose and revaccination groups, respectively), declined at Year 1, but remained above pre-additional vaccination levels thereafter. GMC was 64,603.0 mIU/mL 1 month after the second dose in the revaccination group. GMCs in the control group were 8825.4 mIU/mL at Year 1 and 6858.8 mIU/mL at Year 6. The frequency of gE-specific CD4[2+] T-cells and memory B-cells followed a similar pattern. Pain and fatigue were the most common solicited adverse events. No serious adverse events related to RZV were reported. Conclusions A single additional RZV dose elicited strong and durable humoral and cell-mediated anamnestic responses, with a reactogenicity and safety profile as established in primary studies.