Potential cost-effectiveness of adjuvanted herpes zoster subunit vaccine for older adults in Hong Kong

Background: Adjuvanted herpes zoster (HZ) subunit vaccine is recommended for adults aged ≥50 years. This study aimed to investigate cost-effectiveness of HZ subunit vaccine for older adults at different age in Hong Kong. Methods: A life-long Markov model was designed to simulate outcomes of four alternatives: Vaccination at model entry (age 50 years); deferring vaccination to 60 years; deferring vaccination to 70 years; and no vaccination. Outcome measures included direct cost, indirect cost, HZ and post-herpetic neuralgia incidences, quality-adjusted life years (QALYs) loss, and incremental cost per QALY saved (ICER). Model clinical inputs were derived from literature. HZ treatment costs were collected from a cohort of HZ patients (n = 218). One-way and probabilistic sensitivity analyses were performed. Results: In base-case analysis, vaccination at 50 years showed highest QALYs saved and increment cost (0.00258; USD166), followed by deferring to 60 years (0.00215 QALYs saved; USD102) and deferring to 70 years (0.00134 QALYs; USD62) when comparing to no vaccination. ICERs of vaccination arms versus no vaccine (46,267–64,341 USD/QALY) were between 1–3 × gross domestic product (GPD) per capita in Hong Kong (USD43,530–USD130,590). One-way sensitivity analyses found vaccine cost to be the common and most influential parameter for ICER of each vaccination strategy to become <1 × GDP per capita. In probabilistic sensitivity analysis, vaccination at 50 years, deferring to 60 years and 70 years were accepted as cost-effective in 90% of time at willingness-to-pay (WTP) of 78,400 USD/QALY, 57,680 USD/QALY and 53,760 USD/QALY, respectively. Conclusions: Cost-effectiveness of each strategy is highly subject to the vaccine cost and WTP threshold per QALY saved.