Duration of Antiviral Prophylaxis and Risk of Herpes Zoster among Patients Receiving Autologous Hematopoietic Stem Cell Transplants: A Retrospective, Observational Study

INTRODUCTION There are no real-world data on antiviral prophylaxis (AP) duration and risk of herpes zoster (HZ) given AP duration in patients receiving autologous hematopoietic stem cell transplants (auto-HSCT). The objectives of this study are to describe the duration of AP and to compare incidence of HZ by AP duration in auto-HSCT patients. METHODS This is a retrospective, observational database (Marketscan®) study. This study included patients ≥18 years old who had auto-HSCT during 2009-2013, had chemotherapy within 60 days prior to auto-HSCT (latest chemotherapy date within the 60 days was the study enrollment date), and had continuous health plan enrollment for at least 365 days before and after the study enrollment date. AP duration was the sum of days supply of all AP prescriptions from 30 days before to 365 days after the study enrollment date. Patients were followed from the study enrollment date to the end of continuous health plan enrollment, death, or December 31, 2014 to assess HZ incidence. The Cox proportional hazards model was used to examine the association between the risk of HZ and AP duration. RESULTS This study identified 1959 eligible auto-HSCT patients, of whom 93.0% were prescribed AP. Average AP duration was 220 days (SD = 122), while 200 (11%) patients had AP for ≥1 year. HZ incidence was 42.4/1000 person-years (PY) (95% CI 36.5, 49.0) for the overall auto-HSCT cohort. Among patients who received AP, duration of AP prescriptions and HZ incidence were inversely related. Compared with patients who were on AP for 1-89 days, patients with AP duration of 180-269 days [hazard ratio (HR) = 0.576, p = 0.019], 270-359 days (HR = 0.594, p = 0.023), and ≥360 days (HR = 0.309, p < 0.001) had significantly lower risk of HZ. CONCLUSION Auto-HSCT patients are at increased risk for HZ, even when prescribed AP. A safe and effective vaccine against HZ for auto-HSCT patients could be a useful adjunctive prevention strategy.