This study is an open-label phase Ⅳ clinical trial of the inactivated SARS-CoV-2 vaccine(CoronaVac)manufactured by Sinovac Research & Development Co., Ltd. The purpose of this study is to evaluate the immunogenicity and safety of the Inactivated SARS-CoV-2 Vaccine (Vero Cell) in Healthy Population Aged From 18 to 59 Years.

This study is an open-label phase Ⅳ clinical trial in healthy adult aged 18-59 years. The experimental vaccine was manufactured by Sinovac Research and Development Co.,Ltd.. A total of 1400 subjects will be enrolled,the safety and immunogenicity of booster immunization were evaluated in 400 subjects (group A) who received two doses of primary immunization at an interval of 21 to 31 days. And the safety of booster immunization was evaluated in the extended safety group (group B), which included 1000 subjects.

Inclusion Criteria:

• Healthy adults aged 18-59;
• Have been received two doses of inactivated SARS-CoV-2 vaccine(CoronaVac)manufactured by Sinovac Research & Development Co., Ltd at an interval of 21 to 31 days for group A.Have been vaccination two doses of inactivated SARS-CoV-2 vaccine(CoronaVac)manufactured by Sinovac Research & Development Co., Ltd for group B;
• The subjects can understand and voluntarily sign the informed consent form;
• Proven legal identity.

Exclusion Criteria:

• History of SARS-CoV-2 infection;
• Any serious adverse reactions that are causally related to vaccination during the primary immunization of the previous inactivated SARS-CoV-2 vaccine;
• Severe allergic reactions after primary immunization (including urticaria/rash within 30 minutes after vaccination);
• Autoimmune disease or immunodeficiency / immunosuppression;
• Severe chronic diseases, severe cardiovascular diseases, hypertension and diabetes that cannot be controlled by drugs, liver or kidney diseases, malignant tumors, etc;
• Severe neurological disease (epilepsy, convulsions or convulsions) or mental illness;
• Immunosuppressive therapy, cytotoxic therapy, inhaled corticosteroids (excluding allergic rhinitis corticosteroid spray therapy, acute noncomplicated dermatitis superficial corticosteroid therapy) within 6 months before primary immunization and before booster immunization;
• Already pregnant or are breastfeeding, planning to get pregnant (according to subjects' self-report and urine pregnancy test results)
• Receipt of attenuated live vaccines within 14 days prior to booster vaccination;
• Receipt of inactivated or subunit vaccines within 7 days prior to booster vaccination;
• Acute diseases or acute exacerbation of chronic diseases within 7 days prior to booster vaccination;
• Axillary temperature >37.0°C prior to booster vaccination;
• According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial