Real-world effectiveness of varicella vaccination in Guangzhou, China, 2017-2022: a matched case-control analysis.

Background: China has yet to implement a nationwide two-dose vaccination strategy. This study assesses the real-world effectiveness of varicella vaccination in Guangzhou, where the policy recommends voluntary, self-funded administration of two doses of the live attenuated vaccine, to provide insights for optimizing vaccination strategies.

Research design and methods: Using outbreak data from 2017 to 2022 across preschools, primary, and secondary schools, we employed a three-level matched case-control design (school, grade, and class) and applied conditional logistic regression to estimate the effectiveness of single-dose (VE1) and two-dose (VE2) vaccinations, incremental VE, and the effectiveness of emergency vaccination.

Results: From 2017 to 2022, 1,058 varicella cases were included in the study, with a median age of 9.0 years. The effectiveness of a single-dose vaccine ranged from 45.8% to 46.7%, while the two-dose vaccine showed higher effectiveness (94.5% to 95.8%), with an incremental VE of 89.7% to 92.1%. VE1 decreased over time, whereas VE2 remained relatively high within five years after the booster dose, with the interval between doses having little effect on VE2. Emergency vaccination was effective for the first dose (78.0%-84.5%) and more effective for the second dose (87.2%-91.4%).

Conclusions: Single-dose varicella vaccination provides limited protection, whereas the two-dose regimen enhances effectiveness.