A PhaseⅡ Study to Evaluate the Safety & Immunogenicity of SARS-CoV-2 Alpha/Beta/Delta/Omicron Variants COVID-19 Vaccine (SCTV01E)

Inclusion Criteria: The age when signing ICF should meet the requirements of the scheme (Group A ≥18 years old; Group B 12-17 years old; Group C, 3-11 years old) male or female; Have previously received the recommended dose and immunization procedures of COVID-19 vaccine approved for domestic market, and the interval between signing ICF and receiving the last dose of COVID-19 vaccine is 6-24 months; Subject and/or guardian or client of both parties are able to sign a written ICF and voluntarily participate in the trial, fully understand the trial procedure, the risks of participating in the trial and the alternative interventions available to non-participants; The subject and/or the guardian or client of both parties can read, understand and fill in the diary card; Healthy subjects or subjects with stable underlying diseases. Stable underlying diseases were defined as those who were in stable condition at least 3 months before inclusion in the study, had no significant change in treatment regimen and had not been admitted to hospital due to disease progression; Fertile men and women of childbearing age voluntarily agree to take effective contraceptive measures from signing the ICF to 180 days after receiving the trial vaccine; Pregnancy tests for women of childbearing age during the screening period were negative. Exclusion Criteria: Fever (> 14 years of age, axillary temperature ≥37.3℃; ≤14 years old, axillary temperature ≥37.5℃); SARS-CoV-2 nucleic acid test was positive during the screening period; Previous history of allergy to any vaccine or drug, such as: allergy, urticaria, severe skin eczema, dyspnea, laryngeal edema, angioneurotic edema, etc.; Those who have a history of immune deficiency diseases, major organ diseases, immune diseases [including Guillain-Barre syndrome (GBS), systemic lupus erythematosus, rheumatoid arthritis, asthenia or splenectomy caused by any circumstances, and other immune diseases that researchers believe may have an impact on the immune response], etc.; Currently suffering from severe or uncontrollable cardiovascular diseases, endocrine diseases, diseases of the blood and lymphatic systems, diseases of the liver and kidney, diseases of the respiratory system, diseases of the metabolic and skeletal systems or malignancies (other than basal cell carcinoma of the skin and carcinoma in situ of the cervix), such as severe heart failure, severe pulmonary heart disease, unstable angina, liver failure or uremia; The subjects are in an acute state of disease, such as acute onset of chronic heart failure, acute sore throat, hypertensive encephalopathy, acute pneumonia, acute renal insufficiency, acute cholecystitis, etc.; Anti-tuberculosis therapy is being used; Influenza vaccine within 14 days prior to vaccination or another type of vaccine within 28 days prior to vaccination; Use of immunosuppressant or immunomodulatory drugs for ≥14 days in the 6 months before enrollment, but short-term use of oral, inhaled and topical steroid hormones (≤14 days) is allowed; are pregnant or breastfeeding or plan to become pregnant during the study period; HIV-positive patients;