Is it time for Universal Varicella Vaccination in Chile? A health economic analysis

Abstract

Background: Although the Latin American Society of Pediatric Infectious Diseases (SLIPE) recommended adoption of Universal Varicella Vaccination (UVV) in 2016, UVV is not offered in Chile. In this study, we evaluate the health and economic impact of introducing UVV in Chile. Methods & Materials: A dynamic transmission model of varicella infection with proportionate mixing in a static population and force of infection varying over age, time, and vaccination status was adapted. Seroprevalence data from Argentina, indicating relatively low varicella virus transmission (with 15% of adults never been exposed to natural varicella), were used for calibration in the absence of available Chilean data. Healthcare resource utilization and costs were estimated from a recent study of the clinical characteristics and economic costs of hospitalized varicella patients in Chile. The Chilean immunization schedule currently has vaccination visits at 12 months, 18 months, and 6 years of age during which varicella vaccination could be offered; the following one- (1D) and two-dose (2D) vaccination strategies were considered (age at vaccination/vaccination coverage %): 1D-Early (12m/90%); 1D-Late (18m/85%); 2D-Early-Short (12m/90%, 18m/85%); 2D-Early-Long (12m/90%, 6y/85%); 2D-Late-Long (18m/85%, 6y/85%). Costs were evaluated in 2017 United States Dollars (USD) (1 USD = 633.527 Chilean Pesos). Costs and benefits were discounted at 3%; a 25-year time horizon was used. Results: The model estimates 185,419 varicella cases/year (incidence rate 1023/100,000) in Chile in the absence of UVV with 28 deaths per year. All vaccination strategies were cost saving. The most cost-saving strategy is 1D-Early. 1D-Early UVV will reduce the varicella case load by 87%/99.4%/99.5%/99.7% at 1/5/10/25 years after vaccination, and is estimated to save 3.6M/52M/109M/269M USD (discounted) respectively. Two-dose strategies are more effective, but more costly. Although two-dose strategies are cost effective compared to not vaccinating, the marginal incremental cost effectiveness compared to one-dose strategies is very high. 2D-short is the most effective and cost effective of the two-dose strategies, and can reduce breakthrough varicella by 65-75% compared to one-dose strategies. Conclusion: Both one- or two-dose UVV is estimated to be cost-saving in Chile. Because of historically low varicella transmission rates, UVV can rapidly and sustainably reduce the burden of varicella in Chile.