This is Phase 4 clinical trial of live attenuated varicella vaccines manufactured by Sinovac (Dalian) Vaccine Technology Co., Ltd .The purpose of this study is to evaluate the protective effect of varicella vaccine in children aged 1-12 years and the correlation between varicella antibody and protective effect,to evaluate the immunogenicity and safety of varicella vaccine in children aged 1-12 years.

This study is Phase Ⅳ clinical trial.The experimental vaccine manufactured by Sinovac(Dalian) Vaccine Technology Co., Ltd.This clinical trial consists of four parts,and A total of 45400 subjects will be enrolled.

Study 1,45000 subjects including 15000 subjects aged 1-3 years with no history of varicella vaccination ,15000 subjects aged 4-6 years with a history of 1 dose of varicella vaccine,15000 subjects aged 7-12 years with a history of 1 dose of varicella vaccine will be enrolled to evaluate protective effect of varicella vaccine. There will be 7500 subjects in the experimental group and 7500 in the control group in each age group.And subjects who voluntarily receive varicella vaccine will be included in the experimental group and other subjects will be included in the control group.All subjects in the experimental group will receive one dose of varicella vaccine.

Study 2,400 healthy children including 100 subjects aged 1-3 years with no history of varicella ,150 subjects aged 4-6 years(50 children with no history of varicella vaccination and 100 children with a history of one dose of varicella vaccine),150 subjects aged 7-12 years (50 children with no history of varicella vaccination and 100 children with a history of one dose of varicella vaccine),each subject will receive one or two doses (0,3 months) of varicella vaccine.

Study 3,30000 subjects from study 1 will be enrolled to conduct safety observation study,all adverse events of all subjects will be collected.

Study 4,Herpes fluid collected from study 1 varicella cases will be used to conduct etiological study on the pathogenic strains of varicella cases.

Study 1: Inclusion criteria for a protective effect study of varicella vaccine:

• Healthy children aged 1-12 years without a history of varicella;
• The subjects and/or guardians can understand and voluntarily sign the informed consent form (For subjects aged 8 years and above, both subjects and guardians need to sign the informed consent form);

Study 2: Inclusion criteria for immunogenicity and safety evaluation of varicella vaccine:

• Healthy children aged 1-12 years without a history of varicella;
• The subjects and/or guardians can understand and voluntarily sign the informed consent form (For subjects aged 8 years and above, both subjects and guardians need to sign the informed consent form);
• The subjects and their guardians voluntarily participate in the study and are able to follow all study procedures;
• Proven legal identity.

Study 3: Inclusion criteria for safety evaluation of mass vaccination of varicella vaccine :

• Healthy children aged 1-12 years without a history of varicella;
• The subjects and/or guardians can understand and voluntarily sign the informed consent form (For subjects aged 8 years and above, both subjects and guardians need to sign the informed consent form);
• The subjects and their guardians voluntarily participate in the study and are able to follow all study procedures;
• Proven legal identity;
• Subjects'guardians can fill in adverse events using mobile apps;

Study 4: Inclusion criteria for etiological study on the pathogenic strains of varicella cases:

• Varicella cases among study 1 enrolled subjects who signed informed consent for biological samples collection.

Exclusion Criteria:

• Received two doses of varicella vaccine from other manufacturers(applied to study 1 exclusion criteria);
• Received two doses of varicella vaccine;
• History of severe allergic reactions to vaccines (e.g.acute anaphylaxis, angioneurotic edema, dyspnea, etc.);
• Any confirmed or suspected immunodeficiency disease, including human immunodeficiency virus (HIV) infection;
• Axillary temperature >37.0°C;
• Receipt of other investigational drugs in the past 30 days;
• Receipt of attenuated live vaccines in the past 28 days;
• Receipt of inactivated or subunit vaccines in the past 7 days;
• According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.