Epidemiological characteristics of varicella in Jiulongpo District, Chongqing, 2015-2024

Objective To investigate the epidemiological characteristics of varicella in Jiulongpo District, Chongqing, from 2015 to 2024, and to provide a scientific basis for formulating targeted prevention and control measures. Methods A descriptive epidemiological method was used to analyze the data on reported varicella cases in Jiulongpo District, Chongqing from 2015 to 2024, and to describe its distribution characteristics. The Holt-Winters multiplicative model was used to predict the number of varicella cases from January to June 2025. Results A total of 10 618 cases of varicella were reported from 2015 to 2024 in Jiulongpo District, with no death. The annual incidence ranged from 54.20/100 000 to 132.98/100 000, with an average annual incidence rate of 85.88/100 000. The incidence of varicella showed a bimodal seasonal distribution, with a major peak occurring from October to December and a secondary peak from May to June. The male-to-female ratio of cases was 1.11 to 1. Most cases occurred among students aged 5-14 years. Cases were reported in all townships, with the top three areas in terms of incidence being Yangjiaping, Huangjueping, and Huayan. All varicella-related public health emergencies occurred in schools, primarily during May-June and October-December, consistent with the overall temporal and population distribution of cases. The Holt-Winters multiplicative model predicted a gradual increase in varicella cases from April to June. Among children aged 1-14 years, the average annual vaccination rate of the first dose of varicella vaccine was 12.03%, showing an initial rise followed by a fluctuating decline (P＜0.001), while the second-dose vaccination rate averaged 8.06%, showing a fluctuating upward trend (P＜0.001). Conclusion From 2015 to 2024, the reported incidence of varicella in Jiulongpo District was higher than the national average. The incidence of varicella showed a bimodal seasonal distribution and mainly affected students aged 5-14 years old. At present, the vaccination coverage remains low, insufficient to form an effective herd immunity. The incidence of varicella is projected to gradually increase between April and June 2025. It is necessary to further strengthen prevention and control measures in key settings such as schools and among student populations, enhance vaccination promotion to improve coverage rates, and utilize national pre-warning software and the Chongqing intelligent epidemic prevention and control system to improve surveillance sensitivity and prevent public health emergencies.