A Study on the Persistence of Immunity Following Two-Dose Varicella Vaccination With Varying Intervals in Chinese Children Aged 2-7 years.

Varicella, a highly contagious disease caused by the varicella-zoster virus (VZV), remains prevalent in China despite the introduction of the varicella vaccine in 1997. The current vaccination protocol in China involves a voluntary, self-funded single-dose regimen. This study aims to investigate the longevity of immune response in Chinese children following two-dose varicella vaccination administered at different intervals, with the objective of optimizing vaccination strategies. This 4-year prospective cohort observational study categorized participants into three groups based on the interval between the two varicella vaccine doses: 1-, 3-, and 5-year intervals. Antibody detection was performed using enzyme-linked immunosorbent assay (ELISA). The temporal evolution of IgG antibody levels following the two-dose vaccination was analyzed using a binary logistic regression model with restricted cubic splines (RCS). The study revealed a significant decline in both seropositivity rates and geometric mean concentrations (GMC) over time following the two-dose vaccination. Seropositivity rates decreased from 100.0% to 79.8%, while GMC dropped from 575.1 to 251.9 mIU/mL. No statistically significant differences were observed in seropositivity rates or GMC among the different interval groups (p > 0.05). The RCS-fitted model demonstrated an "inverted U-shaped" relationship between the time since the last vaccination and seropositivity. Antibody levels peaked approximately 22 months after the second dose, with the odds ratio (OR) for antibody concentrations ≥ 50 mIU/mL exhibiting a nonlinear trend in relation to time post-immunization (poverall < 0.001, pnonlinear ≤ 0.001). While the interval between vaccine doses did not significantly impact long-term immune response, a critical turning point in antibody levels was observed at approximately 22 months postvaccination. Furthermore, enhanced long-term monitoring of postvaccination immune responses, particularly beyond the identified turning point, is recommended to facilitate the evaluation and optimization of existing vaccination protocols.