This an open-label phase Ⅳ clinical trial of live attenuated varicella vaccine manufactured by Sinovac (Dalian) Vaccine Technology Co., Ltd.The purpose of this study is to evaluate the immunity persistence of live attenuated varicella vaccine at 6 and 10 years after booster dose.

A total of 792 subjects aged 2 to 6 years including in per-protocol set (PPS) of immunogenicity assessment from previous phase Ⅲ clinical trial were enrolled. About 3.0ml of venous blood was collected at 6 and 10 years after booster immunization for antibody detection.

Inclusion Criteria:

• Subjects in PPS of previous phase Ⅲ clinical trial of varicella vaccine;
• The subjects and/or guardian can understand and voluntarily sign the informed consent form;
• Proven legal identity.

Exclusion Criteria:

• Beyond the blood collection window period;
• History of varicella or shingles;
• History of varicella vaccination since phase Ⅲ clinical trial;
• According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.