This an open phase Ⅳ clinical trial of live attenuated varicella vaccines 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 5 and 8 years after primary immunization with live attenuated varicella vaccine.

This study is an open phase Ⅳ clinical trial in subjects who enrolled in the clinical trial and included in the immunogenicity subgroup PPS set from August to September 2016 .The experimental vaccine and placebo (Freeze Dired Dilution) were manufactured by Sinovac (Dalian) Vaccine Technology Co., Ltd.A total of 703 subjects will be enrolled including 349 subjects in experimental group and 354 subjects in control group .And 3.0-3.5ml of venous blood was collected from all subjects at 5 and 8 years after primary immunization, and the serum was separated for varicella antibody detection. The window period of blood collection was six months.

Inclusion Criteria:

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

Exclusion Criteria:

• History of chickenpox or shingles;
• History of varicella vaccination since phase Ⅲ clinical trial;
• Autoimmune disease or immunodeficiency / immunosuppression;
• History of immunosuppressive therapy 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.