Epidemiological analysis of varicella antibody levels and varicella outbreak surveillance in Pudong New Area, 2023–2025

Varicella-zoster virus (VZV) infection remains a common public health concern among children and adolescents globally, posing a continued threat to population health. To investigate the VZV antibody levels among healthy residents in Pudong New Area, Shanghai, and to analyze the epidemiological characteristics of reported varicella cases and outbreaks, this study provides a scientific basis for the optimization of varicella prevention and control strategies. Descriptive epidemiological methods were used to analyze the varicella IgG antibody positive rate and geometric mean concentration (GMC) of VZV antibodies stratified by age, sex, year, and household registration status, as well as the epidemiological characteristics of reported cases and varicella outbreaks. Multivariable logistic regression was performed to identify factors associated with VZV antibody seropositivity. A total of 1,003 serum specimens were tested, comprising 508 males and 495 females, with a median age of 9.16 years. The overall varicella IgG antibody positive rate was 59.12%, and the GMC was 90.61 mIU/mL. Among age groups, the highest antibody positive rates were observed in the 40–49 years and ≥ 50 years groups, while the lowest rate was in the 10–14 years group. Multivariable logistic regression analysis showed that the 10–14 years group had significantly lower odds of seropositivity compared with the ≥ 50 years group (OR = 0.012, 95% CI: 0.002–0.096, P < 0.001). During the same period, 5,055 reported varicella cases were recorded via the national surveillance system. Case onset was concentrated in May (10.29%) and October to December (33.08%). Concurrently, 51 varicella outbreaks were reported, including 50 clusters and one public health emergency, involving a total of 436 cases. The majority of outbreaks occurred in middle schools (27/51, 52.94%) and universities (14/51, 27.45%). Among outbreak-related cases, body temperature (χ 2 = 341.076, P < 0.001) and the presence of vesicles (χ 2 = 11.094, P = 0.011) differed significantly across immunization groups, whereas rash did not. Significant disparities in varicella IgG antibody positive rates were observed among healthy residents across different age groups, survey years, and household registration statuses, with the lowest positive rate found in adolescents aged 10–14 years. This age group corresponds to the population primarily enrolled in middle schools, where varicella outbreaks were predominantly concentrated. Targeted attention to the varicella immunization status of students aged ≥ 10 years is crucial for reducing the risk of clustered varicella outbreaks.