Impact of the two-dose varicella vaccination recommendation program and surveillance optimization on epidemiological trends in a megacity in China

To assess the impact of implementing a two-dose varicella vaccine (VarV) immunization recommendation program on the incidence of varicella in Chongqing, China. Monthly reported varicella cases from 2011 to 2023 were extracted from the National Notifiable Diseases Reporting System (NNDRS), alongside the vaccination records from the Chongqing Immunization Planning Information Management System. The interrupted time series analysis (ITS) was employed to study the epidemiological trends of varicella. The average reported annual incidence of varicella in Chongqing was 69.6 per 100,000 population during 2011-2023, with the highest incidence recorded in 2019 (133.9 per 100,000 population) and the lowest in 2011 (21.3 per 100,000 population). Children aged 5-9 y accounted for 34.5% of the total cases. Second-dose coverage of VarV surged from 4.1% in 2018 to 27.5% in 2023 among children aged 4-6 y. The segmented regression model demonstrated that, following the incorporation of varicella into the surveillance system in 2014, there was an upward long-term trend in the reported varicella incidence (β₃ = 0.118, <i>P</i> < .01). Following the implementation of the two-dose VarV recommendation strategy in January 2019, a significant long-term decline trend was observed (β₅ = -0.209, <i>P</i> < .01). The official inclusion of varicella into the notifiable disease surveillance can improve the detection, reporting, and evaluation of varicella cases in real-world settings. The implementation of a two-dose VarV recommendation strategy, along with increased coverage of the second dose, can effectively reduce the varicella incidence. Maintaining sensitive surveillance and adhering to the two-dose vaccination schedule are crucial for controlling varicella epidemics.