Impact of Choices in Cost-Effectiveness Analysis of Recombinant Zoster Vaccine Among 65 Years Old and Older in France

OBJECTIVES: Herpes zoster, also known as shingles, arises from reactivation of varicella zoster virus and manifests typically as a painful, unilateral, vesicular rash. French health technology assessment (HTA) body has specific requirements for modelling in cost-effectiveness evaluation (inputs, structure, etc). Impact of these choices needs to be carefully evaluated especially for prevention assets.

METHODS: We used ZOster ecoNomic Analysis, a multi-cohort Markov model, to assess the cost-effectiveness of the recombinant zoster vaccine (RZV) in older adults in the French setting. One million adults aged ≥65 years were followed for 30 years, considering RZV versus zoster live vaccine (ZVL) or no vaccination. Analyses were conducted under a payer perspective using epidemiological and cost data mainly based on local studies and a 2.5% discount rate. HTA body questioned different choices in our initial proposal, among which vaccine coverage, efficacy or quality of life data. We describe the level of impact on incremental cost-effectiveness ratio (ICER).

RESULTS: Among the factors, exploring 70% 2nd dose RZV coverage instead of 100% or considering a network meta-analysis for vaccine efficacy when comparing RZV to ZVL instead of a naïve comparison had little impact (<5% variation). Switching from our proposal to use quality-adjusted life-year (QALY) loss derived from literature to clinical trial data favoured by HTA led to a >40% change in ICER.

CONCLUSIONS: Independency of HTA body evaluation is important to guarantee that their decisions are unquestioned. Exploring uncertainty is one of the most difficult exercises in this perspective. This example highlights the various levels of impact of choices (limited to high). Regarding QALY evaluation, the well-controlled clinical trials EQ5D may suffer questionable consistency due to limited sample of patients with the disease. This highlights 1- continued research in this field is needed including in the real-world setting; 2- how important a scientific committee guidance may be.