Abstract: Objective To investigate the epidemiological characteristics of varicella breakthrough cases among children under 14 years of age in Guangyuan City from 2017 to 2022, with the aim of providing a scientific foundation for the prevention and control of varicella. Methods Data on varicella breakthrough cases in children under 14 were collected for the period 2017-2022 in Guangyuan City. Descriptive epidemiological methods were employed to analyze the characteristics of these cases. Pearson correlation analysis was utilized to assess the relationship between the age at initial vaccination and the interval from vaccination to disease onset. Results From 2017 to 2022, a total of 957 breakthrough cases were reported in Guangyuan City among children under 14, constituting 25.30% of all reported varicella cases. The proportion of breakthrough cases demonstrated a significant increase (c²_{for trend}=130.283, P<0.01). Statistically significant variations in the proportion of breakthrough cases were identified across different months, districts, occupations, and age cohorts (all P<0.01). The incidence exhibited a bimodal distribution with peaks from May to July and from October to December. The majority of cases were reported in Lizhou District (53.29%) and among students (82.76%), with a male-to-female ratio of 1.10: 1. A total of 852 and 105 breakthrough cases were reported in recipients of one and two vaccine doses, respectively. The median interval from vaccination to onset was 8.00 (IQR: 5.84, 9.85) years for single-dose recipients and 4.15 (IQR: 2.30, 6.06) years for two-dose recipients. The difference in the temporal distribution of onset post-vaccination between the one-dose and two-dose groups was statistically significant (c²=14.737, P<0.01). A significant negative correlation was observed between the age at first-dose vaccination and the interval to disease onset (r=-0.236, P<0.01). The incidence rate among unvaccinated individuals was 963.29 per 100 000, whereas the breakthrough infection rate among vaccinated individuals was 316.74 per 100 000. The overall vaccine effectiveness (VE) was calculated to be 69.01%. The VE for the one-dose and two-dose schedules was 63.96% and 85.51%, respectively. Conclusions The proportion of varicella breakthrough cases relative to total varicella incidence among children under 14 in Guangyuan City is on an upward trend. Varicella vaccination is effective in reducing disease incidence, with a two-dose vaccination schedule affording substantially greater protection against varicella than a single-dose regimen.

Key words: Varicella, Breakthrough cases, Epidemiological characteristics, Vaccine effectiveness