BACKGROUND Herpes zoster (HZ) infection of hematopoietic stem cell transplant (HSCT) patients is of clinical concern. Vaccination could help restore immunity to varicella zoster virus (VZV); however, temporal changes in immunogenicity and safety of live HZ vaccines after HSCT is still unclear. The aim of this study was to elucidate the temporal immunogenicity and safety of the HZ vaccine according to time since HSCT and to determine optimal timing of vaccination.

METHODS Live HZ vaccine was administered to patients 2-5 years or > 5 years post-HSCT. Control groups comprised patients with a hematologic malignancy who received cytotoxic chemotherapy and healthy volunteers. Humoral and cellular immunogenicity were measured using a glycoprotein enzyme-linked immunosorbent assay (gpELISA) and an interferon-γ (IFN-γ) enzyme-linked immunospot (ELISPOT) assay. Vaccine-related adverse events were also monitored.

RESULTS Fifty-six patients with hematologic malignancy (41 in the HSCT group and 15 in the chemotherapy group) along with 30 healthy volunteers were enrolled. The geometric mean fold rises (GMFRs) in humoral immune responses of the 2-5 year and > 5 year HSCT groups, and the healthy volunteer group, were comparable and significantly higher than that of the chemotherapy group (3.15, 95% CI [1.96-5.07] vs 5.05, 95% CI [2.50-10.20] vs 2.97, 95% CI [2.30-3.83] vs 1.42, 95% CI [1.08-1.86]). The GMFR of cellular immune responses was highest in the HSCT 2-5 year group and lowest in the chemotherapy group. No subject suffered clinically significant adverse events or reactivation of VZV within the follow-up period.

CONCLUSION Our findings demonstrate that a live HZ vaccine is immunogenic and safe when administered 2 years post-HSCT.