Cost-effectiveness analysis of varicella vaccine as post-exposure prophylaxis in Hong Kong

Objectives: The varicella vaccine is an effective post-exposure prophylaxis (PEP) for chickenpox. This study aimed to analyze the cost-effectiveness of PEP using varicella vaccine for pediatric patients from the perspective of the public healthcare provider in Hong Kong. Methods: A decision tree was designed to compare cost and clinical outcomes of PEP with varicella vaccine versus no PEP in pediatric patients (aged 1-18 y) susceptible to chickenpox with household exposure. Two tiers of outcome were simulated: (1) total direct medical cost per subject exposed, and (2) the quality-adjusted life-year (QALY) loss associated with chickenpox per subject exposed. Model inputs were retrieved from local epidemiology and the medical literature. A sensitivity analysis was performed on all parameters to test the robustness of model results. Results: The base-case analysis showed PEP with varicella vaccine to be less costly (expected cost USD 320 vs USD 731) with lower QALY loss (0.00423 QALY vs 0.01122 QALY) when compared to no PEP. The sensitivity analysis showed that PEP with varicella vaccine was less costly if PEP effectiveness was >6.2% or the chickenpox infection rate without PEP was >8.6%. In 10,000 Monte Carlo simulations, PEP with vaccine was cost-effective over 99% of the time, with a mean cost saving of USD 611 per patient (95% confidence interval USD 602-620; p < 0.001) and lower mean QALY loss of 0.00809 QALY (95% confidence interval 0.00802-0.00816 QALY; p < 0.001). Conclusions: Using varicella vaccine as PEP appears to be a cost-saving strategy to avert QALY loss in susceptible pediatric patients exposed to chickenpox in Hong Kong.