Impact of a two-dose varicella vaccination strategy and public health measures on varicella incidence in Shengzhou City: An interrupted time series study.

This study aims to evaluate the impact of a two-dose varicella vaccine immunization strategy and public health and social measures (PHSMs) on varicella incidence in Shengzhou City. In this study, PHSMs are defined as non-pharmaceutical interventions - including social distancing, school closures, and case isolation - implemented during the COVID-19 pandemic. Data on reported varicella cases in Shengzhou City from 2006 to 2022 were collected, and interrupted time series regression models were constructed to assess changes in monthly varicella incidence rates during the periods of the one-dose strategy, the two-dose strategy, and the implementation of PHSMs. Interrupted time series analyses showed a significant immediate reduction in monthly varicella incidence of 0.754 per 100,000 (P = .023) following the introduction of the two-dose varicella vaccine strategy. A further immediate reduction of 1.363 per 100,000 (P = .001) occurred after the implementation of PHSMs. Regarding long-term trends, monthly varicella incidence declined by 0.009 per 100,000 (P = .284) following the two-dose strategy, though this change was not statistically significant. In contrast, a significant increase of 0.041 per 100,000 (P = .001) was observed after the implementation of PHSMs. Our findings suggest that while the two-dose strategy led to an immediate decline in varicella incidence, it did not demonstrate a statistically significant impact on the long-term upward trend within the study period. This may reflect the time required to achieve sufficient population immunity, limitations in surveillance sensitivity, or other unmeasured ecological factors. PHSMs provided short-term suppression but were insufficient to alter long-term transmission dynamics. Sustained high coverage with the two-dose schedule remains essential, and continued monitoring is warranted.