Effectiveness of Universal Varicella Vaccination after ten years of implementation in Tuscany (Central Italy)

Varicella vaccination is currently recommended in several European countries, including Italy. Tuscany Region introduced Universal Varicella Vaccination (UVV) in 2008, and it was later included in the Italian National Immunization Plan 2017-2019. Recently, it has also been made mandatory in Italy for school attendance. The aim of our study was to assess the effectiveness of the UVV program in preventing varicella cases and related hospitalizations in children born between 2008 and 2017, during the pre-pandemic period (2010-2019) in Tuscany (Central Italy). We applied the screening method to assess varicella vaccine effectiveness (VE) for the first and the second vaccine dose in the birth cohorts targeted by the UVV. We considered the vaccination coverage (VC) at 24 months and at 5-6 y of age, and we verified the vaccination status of each notified or hospitalized case to identify breakthrough varicella cases (BV). We assessed a VE of 84.8% (95%CI:83.5-85.9%) for at least one varicella vaccine dose and 95.7% (95% CI: 93.6-97.1%) for the second dose in preventing notifications. VE in preventing hospitalizations was 98.5% (95% CI: 96.7-99.3%) after one dose and 100% after two doses. The median time interval between the first or second vaccine dose and the onset of varicella was 34 months and 28 months, respectively. Our study demonstrated the excellent vaccine effectiveness profile of the vaccines used over a 10-y period in Tuscany, in preventing notified and hospitalized varicella cases in the target cohorts of children, confirming the health benefits of the UVV in Central Italy.