Optimal gender-specific age for cost-effective vaccination with adjuvanted herpes zoster subunit vaccine in Chinese adults

Background 
Adjuvanted herpes zoster (HZ) subunit (HZ/su) vaccine is recommended for healthy adults aged 50 years, yet vaccine efficacy is expected to wane over time. Age-sex specific cost-effectiveness analyses of HZ/su vaccine are warranted to inform decision-making on vaccine policy. We aimed to determine the optimal gender-specific age for cost-effective HZ/su vaccination in Hong Kong. 
Methods 
A Markov model was used to compare outcomes with and without HZ/su in healthy males and females at age 50–80 years. Model outcome measures were total cost, HZ cases, and HZ-associated quality-adjusted life-years (QALYs) loss. Incremental cost per QALY saved (ICER) by HZ/su was estimated for each age-sex group. Sensitivity analyses were performed to examine robustness of model results. 
Results 
HZ/su reduced incidence of HZ in both males and females aged 50–80 years and the numbers needed to vaccinate to avoid one HZ case were lowest at age 60 years for males (6.05) and females (5.50). The highest QALY-saved occurred in females (0.00396 QALYs) and males (0.00379 QALYs) who were vaccinated at 60 years old. The ICERs were lowest at age 60–70 years for both genders. Using 1× gross domestic product per capita of Hong Kong (USD46,153) as willingness-to-pay threshold, HZ/su vaccine was accepted to be cost-effective for all female and male age groups at vaccine cost = USD160, for female aged 50–79 years and male aged 54–74 years at vaccine cost = USD200, and for female aged 59–71 years at vaccine cost = USD240. 
Conclusions 
HZ/su vaccine is more likely to be cost-effective for males and females aged between 60–70 years than the extreme age groups (less than 60 years and older than 70 years) in Hong Kong. The age range for cost-effective acceptance of HZ/su vaccine appears to be broader in females than males given the same vaccine cost and willingness-to-pay threshold.