Epidemiological characteristics of varicella and factors associated with breakthrough varicella among children aged 0–14 years in Jiangsu Province, China

Background This study aimed to explore the epidemiological characteristics of varicella and breakthrough varicella (BV), as well as factors associated with the BV proportion during 2021–2024.Research design and methods Data on varicella cases aged 0–14 years were extracted from the national surveillance system and linked to individual immunization records. Logistic and linear regression were adopted.Results Among 162,844 cases, 34.3% were BV, and 10–14-year age group increased significantly from 24.7% in 2021 to 61.1% in 2024 (p < 0.001). During 2023–2024, older age groups showed lower BV proportion (5–9 years: OR = 0.49; 10–14 years: OR = 0.58; both p < 0.001), while the 10–14 years group showed higher BV proportion (OR = 1.08, p < 0.001) during 2021–2022. Autumn onset (OR = 1.14) and cases from central (OR = 1.39) and southern Jiangsu (OR = 2.31) were positively associated with BV proportion (all p < 0.001). The median breakthrough interval among one-dose recipients was 7.5 years, with 61.7% of cases occurring ≥6 years post-vaccination.Conclusion Varicella burden in Jiangsu is shifting to older children. Strengthening two-dose varicella vaccination and maintaining routine vaccination coverage in young children are crucial for varicella control.