Safety and Immunogenicity of Recombinant COVID-19 Variant Vaccine (Sf9 Cell) as a Booster

Inclusion Criteria: * 1\. Voluntarily sign the ICF approved by the Ethics Committee and agree to participate in the study before any study procedure. * 2\. Healthy males or females able to provide legal identification, aged 18 years and above at the time of signing ICF. * 3\. Subjects who have completed homologous primary vaccination with either Inactivated or mRNA or Viral Vector COVID-19 vaccines (full approval, CMA or EUA) and have the last dose administered 6 months ago or earlier from the date of signing the ICF for the study. Those who have received combined immunization with two doses of vaccines should be excluded. * 4\. Able to communicate well with the investigator, and able to understand and comply with the requirements of this clinical trial. * 5\. Males with female sexual partners or females of childbearing potential voluntarily take effective contraceptive methods from signing ICF to 3 months after the vaccination, including sexual abstinence or effective contraceptive measures (e.g., intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, intrauterine device (IUD), condoms (male), diaphragm, and cervical cap). * 6\. Axillary temperature \<37.3℃. Exclusion Criteria: * 1\. Positive SARS-CoV-2 RT-PCR at screening. * 2\. Prior medical history of Serve Acute Respiratory Syndromes (SARS), Middle East Respiratory Syndrome (MERS) and other human coronavirus infections or diseases. * 3\. Prior history or family history of convulsion, epilepsy, encephalopathy and psychosis. * 4\. Fear of needles. * 5\. Pregnant or lactating females or those who plan to become pregnant or donate eggs during study period. * 6\. Prior history of allergic reaction or anaphylaxis to any vaccine or its excipients, e.g., hypersensitivity, urticaria, serious eczema, dyspnea, laryngeal edema, and angioedema etc.. * 7\. Prior use of any vaccine within 28 days before receiving this investigational vaccine or planning to use any vaccine other than this investigational vaccine during the study period. * 8\. Participation in studies of any other interventional device or drug within 28 days before the screening, or current treatment with other investigational drug(s) or within 5 half-lives after taking the last dose of the study drug. * 9\. Hereditary hemorrhagic tendency or coagulation dysfunction (e.g., clotting factors deficiency, coagulation disorders or platelet disorders), or a history of severe bleeding, or a history of massive bleeding after intramuscular injection or venipuncture, or a history of ecchymosis. * 10\. Known medical history or diagnosis confirming that subjects have diseases affecting immune system function, including cancer, congenital or acquired immunodeficiency (e.g., infection with Human Immunodeficiency Virus (HIV)), or uncontrolled autoimmune disease. * 11\. Serious or uncontrolled respiratory system disorders, cardiovascular disorders, nervous system disorders, blood and lymphatic system disorders, liver and kidney disorders, metabolism and skeletal disorders, etc. influencing study results evaluation at the investigator's discretion. * 12\. Asplenia or functional asplenia. * 13\. Long-term use (continuous use for ≥14 days) of immunosuppressants or other immunomodulators (e.g., glucocorticoids: prednisone or equivalents) within 6 months prior to administration of this investigational vaccine, except for topical medications (e.g., ointments, eye drops, inhalants or nasal sprays). And the topical medications should not exceed the recommended dose in the labels or induce any signs of systemic exposure. * 14\. Having received immunoglobulins and/or blood products within 3 months prior to administration of this investigational vaccine. * 15\. History of tuberculosis treatment or currently on antikoch's treatment for tuberculosis, whether pulmonary or extrapulmonary. * 16\. Suspected or known alcohol dependency or drug abuse, which may affect safety evaluation or subject's compliance at the investigator's discretion. * 17\. Planning to permanently move from the local area before study completion or leave the local area for a long time during the period of study visits. * 18\. An employee of the study site, Sponsor and contract research organization (CRO) taking part in the study. * 19\. Other conditions unsuitable for this study at the investigator's discretion.