Analytical approach:
The analysis was based on a discrete-event simulation model with a lifetime horizon. The authors stated that the study was carried out from the perspective of the Canadian health care payer.
Effectiveness data:
The clinical data came from a selection of relevant studies and country-specific databases, including the Shingles Prevention Study (Oxman, et al. 2005, see ‘Other Publications of Related Interest’ below for bibliographic details), which was a double-blind, randomised placebo-controlled trial. The key input was the efficacy of the vaccination in reducing herpes zoster-related events, and this was from the Shingles Prevention Study. Assumptions on the waning of vaccine efficacy were also needed and were based on data from published observational studies and a large clinical trial.
Monetary benefit and utility valuations:
The utility values were derived from several published studies that used the European Quality of life (EQ-5D) and the Zoster Brief Pain Inventory (ZBPI) questionnaires. The preferences were mainly those of patients with herpes zoster.
Measure of benefit:
Quality-adjusted life-years (QALYs) were the summary benefit measure and they were discounted at an annual rate of 5%.
Cost data:
The economic analysis included the costs of vaccination (acquisition and administration), physician visits, hospitalisations, and drugs for the management of the acute phase of herpes zoster and of post-herpetic neuralgia (PHN). The unit costs and resource quantities were from a Government of British Columbia payment schedule database, a hospital cost model, and published studies. The vaccine cost was from a US source as it was not in use in Canada at the time of this study. The costs were in Canadian dollars (CAD) and were discounted at an annual rate of 5%. The price year was 2008.
Analysis of uncertainty:
A deterministic one-way sensitivity analysis was undertaken on parameters, such as age, vaccine protection length, vaccine cost, PHN length, and proportion of the population with previous varicella zoster virus infection. A probabilistic approach, based on pre-determined probability distributions for the model inputs, was used to generate confidence intervals (CIs) and to construct cost-effectiveness acceptability curves for various willingness-to-pay (WTP) thresholds. The expected value of perfect information was estimated, considering the uncertainty in all parameters, as well as an expected value of partial perfect information, considering the uncertainty in selected inputs.