Inclusion Criteria:  Health subjects aged ≥18 years. Have received two-dose inactivated SARS-CoV-2 vaccine before 6 months or more. The subject can provide with informed consent and sign informed consent form (ICF). The subjects are able to and willing to comply with the requirements of the clinical trial program and could complete the 6-month follow-up of the study.  Exclusion Criteria:  Have the medical history or family history of convulsion, epilepsy, encephalopathy and psychosis. Be allergic to any component of the research vaccines, or used to have a history of hypersensitivity or serious reactions to vaccination. Women with positive urine pregnancy test. Have acute febrile diseases and infectious diseases. Axillary temperature>37.0℃. Have serious cardiovascular disease, such as arrhythmia, conduction block, myocardial infarction, severe hypertension that cannot be controlled by medication (systolic blood pressure ≥180mmHg and/or diastolic blood pressure ≥110mmHg when measured in the field). Have severe chronic diseases or condition in progress cannot be smoothly controlled, such as asthma, diabetes, thyroid disease. Congenital or acquired angioedema / neuroedema. Have the history of urticaria 1 year before receiving the investigational vaccine. Have asplenia or functional asplenia. Patients with chronic obstructive pulmonary disease, pulmonary fibrosis and other pulmonary abnormalities. Have history of SARS-CoV-2 infection or COVID-19. Have symptoms of upper respiratory tract infection. Have traveled to medium or high risk areas or traveled abroad in the past 21 days, and epidemiologically contacted with SARS-CoV-2. Any medical, psychological, social, or other conditions that, in the investigator's judgment, are inconsistent with the protocol or affect the subject's informed consent.