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