To analyze the epidemic characteristics of breakthrough cases of varicella in Shapingba District, Chongqing, and provide reference for the prevention and control of the varicella epidemic in the area.

Collect information on varicella cases and their vaccination in Shapingba District from 2019 to 2023, Use descriptive epidemiological methods to analyze the epidemiological characteristics of varicella breakthrough cases, and use linear regression to analyze the relationship between breakthrough cases and age at the time of vaccination and the time interval between vaccination and onset of disease.

From 2019 to 2023, there were a total of 802 breakthrough cases of varicella in Shapingba District, Chongqing, accounting for 14.87% of the total number of varicella cases. The majority of cases were vaccinated with one dose of varicella (648 cases, accounting for 80.80%), and the differences in composition among different years were statistically significant (χ²=16.400,P<0.005); The epidemic has a bimodal distribution, from October to December and May to July each year. The least cases are in winter (142 cases, accounting for 11.68%), and the most cases are in spring (198 cases, accounting for 17.32%). The composition differences between different seasons are statistically significant (χ²=16.348, P<0.001); The breakthrough cases of chickenpox are mainly male, with the highest incidence among primary school students aged 6～10, and the differences in composition are statistically significant (χ²=877.420, P<0.001); The time interval from the first dose of chickenpox vaccine to the onset of breakthrough cases was 46 days to 17 years, with a median \[M(P₂₅,P₇₅)\] of 7 years (4 years, 10 years). The median time interval between scattered children, primary school students, and middle school students was 3 years (2 years,4 years), 8 years (6 years, 9 years), and 12 years (11 years,14 years), respectively, with statistical significance (H=497.280, P<0.001); There is a negative correlation between age at the time of first dose vaccination and the interval between onset of the disease in breakthrough cases, with a correlation coefficient of r=-0.230 (t=-6.693, P<0.001).

Breakthrough cases of varicella in Shapingba, Chongqing are mainly concentrated in primary school students during the start of the school season, with an interval of 7 years between onset. It is necessary to further strengthen the prevention and control of the varicella epidemic in primary schools, further improve the vaccination rate of children with varicella vaccines, and recommend receiving two doses of vaccines before starting primary school to reduce the risk of breakthrough cases.