Impact of two-dose varicella vaccination in Guangzhou: An interrupted time-series study

In November 2017, Guangzhou implemented a self-paid two-dose varicella vaccination program. This study evaluated the program's impact on varicella incidence trends across the general population and specific age groups. An interrupted time-series analysis was conducted using surveillance data from January 2011 to December 2024. The pre-intervention period spanned 2011-2017, and the post-intervention period 2018-2024. Seasonal-trend decomposition and segmented regression were employed to analyze changes in level and trend of varicella incidence. A total of 225,497 varicella cases were reported between 2011 and 2024. The annual incidence rate decreased by 28.1% from the pre-intervention to post-intervention period, from 126.80 to 91.14 per 100,000 population. Prior to intervention, there was no evidence of a monthly change in varicella incidence (0.3%; t = 2.27, <i>P</i> = .294). Significant upward trends were observed among 10-14-y-olds and ≥20-y-olds (0.6% monthly increase, both <i>P</i> < .01). Post-intervention, a significant monthly decrease of 1.8% was observed overall (t = -9.956, <i>P</i> < .001). The most pronounced reduction occurred in 4-6-y-olds (3.8% monthly decrease), followed by 7-9-y-olds (3.0%), 0-3-y-olds (2.3%), 10-14-y-olds (1.9%), ≥20-y-olds (1.1%), and 15-19-y-olds (0.5%). Varicella incidence exhibited consistent seasonal variation, with a primary peak occurring from October to January. The two-dose varicella vaccination program was associated with a significant reduction in varicella incidence across all age groups in Guangzhou, demonstrating both direct protection among vaccinated children and indirect herd effects in older populations. These findings support incorporating the two-dose varicella vaccine into routine national immunization programs.