Modeling the clinical and economic impact of universal varicella vaccination in Belgium with dynamic population.

Although universal varicella vaccination (UVV) significantly reduces morbidity and mortality, it has not been implemented in Belgium. We evaluated the clinical and economic outcomes of two-dose UVV in Belgium. A previously published dynamic transmission model with dynamic population age structure was adapted to Belgium. The base case UVV strategy (Strategy 0) consisted of routine two-dose varicella vaccination at ages 1 year (vaccine coverage rate [VCR] = 95%) and 8 years (VCR = 90%), catch-up one-dose varicella vaccination at 8 years (VCR = 70%, 1-year duration), and routine two-dose herpes zoster (HZ) vaccination at 60 years (VCR = 50%). Alternative vaccination strategies were evaluated and reported. The reference strategy consisted of routine two-dose HZ vaccination only. Outcomes were estimated for a 50-year time-horizon. Annual discounting of 3% and 1.5% were applied to costs (in 2023 Euros) and quality-adjusted life-year outcomes, respectively. Under Strategy 0, cumulative varicella incidence, hospitalizations, and deaths decreased by approximately 91%, 89%, and 61% respectively. A transient increase in HZ incidence (that peaked in 2032 at +3% versus the reference strategy) was observed, however, cumulative HZ cases decreased by 3% over 50 years. Under the payer perspective, Strategy 0 had an incremental cost-effectiveness ratio of €11,260. Under the societal perspective, Strategy 0 resulted in cost savings, with total costs decreasing by €17,524,487. UVV can significantly reduce the burden of varicella with marginal impact on HZ cases and be cost-effective in Belgium versus routine HZ vaccination only.