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

BACKGROUND

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.

RESEARCH DESIGN AND

METHODS

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.

RESULTS

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.

CONCLUSION

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.