Evaluation of varicella outbreak control following implementation of a two-dose free vaccination policy in Wuxi, China (2014–2024)

Varicella is a common vaccine-preventable disease in China, with frequent outbreaks in schools and communities. In late 2018, Wuxi implemented a free two-dose varicella vaccination policy. This study evaluated its epidemiological impact.
We analyzed outbreak data from Wuxi during 2014–2024. Main outcomes included outbreaks, cases, and outbreak duration. Interrupted time series and ARIMA models were used to evaluate temporal trends. Fixed-effects regression examined the association between vaccination coverage and outbreak indicators. Spatial analysis identified clustering patterns before and after policy.
After policy implementation (2019–2024), outbreaks decreased by about 56% and cases decreased by about 60%. Annual percent change shifted from strongly positive before the policy (APC > 140%, p < 0.05) to negative after the policy (APC < −30%, p < 0.05). Each 1% increase in two-dose coverage was associated with reductions of 0.82 outbreaks (p < 0.001), 21.67 cases (p < 0.001), and 2.55 days in duration (p < 0.05). Spatial clustering weakened over time.
The free two-dose vaccination policy was associated with substantial reductions in varicella outbreaks in Wuxi. Sustaining high two-dose coverage remains important. Interpretation should consider the ecological design, lack of individual-level vaccination data, and potential COVID-19-related confounding.