Analysis of sero-epidemiological characteristics of varicella in healthy children in Jiangsu Province, China.

Background: In recent years, outbreaks of varicella have continued to occur, and the coverage rate of varicella vaccine in Jiangsu Province, China, remains unclear. This study aims to analyse the levels of immune antibody against varicella and obtain a comprehensive understanding of the varicella attenuated live vaccine (VarV) coverage rate in children aged 1-9 years in Jiangsu Province.

Methods: From June to October 2016, a cross-sectional survey was conducted to collect 3631 serum samples from healthy children aged 1-9 years in Jiangsu Province. The immunoglobulin G (IgG) antibody levels of varicella were detected by enzyme-linked immunosorbent assay (ELISA).

Results: The VarV coverage rate of healthy children was only 43.1% (95% CI: 41.1-44.7%). The seroprevalence after vaccination with a single dose of VarV was only 57.1%, and the overall seropositivity and geometric antibody titre (GMC) were 43.5% and 225.4 mU/ml, respectively. The seropositivity was significantly higher in girls than in boys (χ = 18.82, P < 0.001). The difference in seropositivity between the 5-9 age group and 1-4 age group was statistically significant (χ = 84.31, P < 0.001). The difference in seropositivity between different regions was statistically significant, with the highest seropositivity in the northern area, 53.7% (χ = 35.64, P < 0.001). The seropositivity in the group receiving one dose of VarV was significantly higher than that of the unvaccinated group (χ = 205.16, P < 0.001). Linear regression analysis suggested that the GMC of varicella antibodies wanes with the time since vaccination (F = 65.01, P = 0.002).

Conclusion: The VarV coverage rate of healthy children in Jiangsu Province was low. Sero-conversion rates were also low after one dose of VarV, and the immune effectiveness of a single dose of VarV was limited. To control the spread of varicella, VarV should be included in the routine immunization program, and strengthened immunization measures for the varicella-susceptible population warrant additional consideration.