Safety and Immunogenicity Study of an Inactivated SARS-CoV-2 Vaccine for Preventing Against COVID-19 in People Aged ⩾60 Years

Inclusion Criteria: * Phase Ib: 1. Healthy people aged ⩾60 years (including boundary values), both men and women. 2. Proven legal identity. 3. Participants should understand the contents of the informed consent form, the vaccine in this trial, voluntarily sign the informed consent form, and be capable of using thermometers, scales, and filling in diary cards and contact cards as required. 4. Participants should be able to communicate well with investigators, understand and comply with the requirements of this trial. 5. Axillary temperature ≤37.0 ℃. * Phase IIb: 1. Healthy people aged ⩾60 years (including boundary values), both men and women. 2. Proven legal identity. 3. Participants should understand the contents of the informed consent form, the vaccine in this trial, voluntarily sign the informed consent form, and be capable of using thermometers, scales, and filling in diary cards and contact cards as required. 4. Participants should be able to communicate well with investigators, understand and comply with the requirements of this trial. 5. Axillary temperature ≤37.0 ℃. Exclusion Criteria: * Phase Ib: 1. Contraindications for vaccination. 2. History of allergy to vaccines or drugs. 3. Immunization with any vaccine within 1 month. 4. Diseases that cannot be controlled by drugs, such as hypertension, diabetes, asthma, etc. 5. Those who developed acute disease within 2 weeks, or had symptoms of fever or upper respiratory tract infection within 7 days. 6. Those who have a hereditary bleeding tendency or coagulation dysfunction, or a history of thrombosis or bleeding disorders. 7. Those who cannot tolerate venipuncture, or have a history of halo needles or halo blood. 8. For any reason, the spleen was removed partially or completely. 9. Those who have undergone surgery within 3 months before signing the informed consent, or those who plan to perform surgery during the trial or within 3 months after the end of the trial (including cosmetic surgery, dental and oral surgery). 10. Those who donated or lost blood (≥200 mL) in the past 3 months, who received blood transfusion or use of blood products, or who planned blood donation during the trial. 11. Receipt of other investigational or unregistered products (drugs, vaccines, biological product or devices) in the past 3 months, or plan to use other investigational or unregistered products during the study. 12. Receipt of immunosuppressive therapy within 6 months before signing the informed consent form, such as long-term systemic glucocorticoid therapy (with systemic glucocorticoid therapy for more than 2 weeks within 6 months, such as prednisone or similar drugs) ), but local administration (such as ointment, eye drops, inhalation, or nasal spray) is allowed. The local administration should not exceed the dosage recommended in the instructions or have any signs of systemic exposure. 13. Those who have took soft drugs (such as marijuana) within 3 months before signing the informed consent form or took hard drugs (such as: cocaine, phencyclidine, etc.) within 1 year before the trial. 14. Those who smoked more than 5 cigarettes per day within 3 months before signing the informed consent form. 15. The weekly drinking volume is greater than 14 units within 3 months before signing the informed consent form (1 unit alcohol approximately equal to 360 mL beer or 45 mL spirits with 40% alcohol content or 150 mL wine). 16. The comprehensive physical examination does not meet the health standards, mainly including: (1) Those with abnormal vital signs with clinical significance. (2) BMI\<18 kg/m\^2 or\> 30 kg/m\^2. (3) Abnormal laboratory examination with clinical significance. (4) Those who tested positive for human immunodeficiency virus (HIV) antibody, hepatitis B surface antigen, hepatitis B e antigen, hepatitis C virus antibody, or Treponema pallidum antibody (tp-trust). 17. Women who have a positive pregnancy test, or men who have a birth plan or plan to donate sperm from the screening to 12 months after the second vaccination. 18. Positive in drug abuse screening during the screening period (Morphine, Methamphetamine, Ketamine, MDMA and Tetrahydrocannabinolic acid). 19. Positive in alcohol breath test during the screening period. 20. Positive in SARS-CoV-2 nucleic acid screening or antibodies (IgG or IgM) screening. 21. History of severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS) or other coronavirus infection (HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1). 22. History of contact with confirmed or suspected cases infected with SARS-CoV-2 within 1 month. 23. Any other situations judged by investigators as not suitable for participating in this study. * Phase IIb: 1. Contraindications for vaccination. 2. History of allergy to vaccines or drugs. 3. Immunization with any vaccine within 1 month. 4. Diseases that cannot be controlled by drugs, such as hypertension, diabetes, asthma, etc. 5. Those who developed acute disease within 2 weeks, or had symptoms of fever or upper respiratory tract infection within 7 days. 6. Those who have a hereditary bleeding tendency or coagulation dysfunction, or a history of thrombosis or bleeding disorders. 7. For any reason, the spleen was removed partially or completely. 8. Those who have undergone surgery within 3 months before signing the informed consent, or those who plan to perform surgery during the trial or within 3 months after the end of the trial (including cosmetic surgery, dental and oral surgery). 9. Those who donated or lost blood (≥200 mL) in the past 3 months, who received blood transfusion or use of blood products, or who planned blood donation during the trial. 10. Receipt of other investigational or unregistered products (drugs, vaccines, biological product or devices) in the past 3 months, or plan to use other investigational or unregistered products during the study. 11. Receipt of immunosuppressive therapy within 6 months before signing the informed consent form, such as long-term systemic glucocorticoid therapy (with systemic glucocorticoid therapy for more than 2 weeks within 6 months, such as prednisone or similar drugs) ), but local administration (such as ointment, eye drops, inhalation, or nasal spray) is allowed. The local administration should not exceed the dosage recommended in the instructions or have any signs of systemic exposure. 12. Women who have a positive pregnancy test, or men who have a birth plan or plan to donate sperm from the screening to 12 months after the second vaccination. 13. History of severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS) or other coronavirus infection (HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1). 14. History of contact with confirmed or suspected cases infected with SARS-CoV-2 within 1 month. 15. The comprehensive physical examination does not meet the health standards, mainly including: (1) Those with abnormal vital signs (Pulse \<55 beats per minute or\> 100 beats per minute at rest, Systolic blood pressure ≥140mmHg or Diastolic blood pressure ≥90mmHg, breathing\> 20 beats per minute or \<12 beats per minute). (2) Those who tested positive for human immunodeficiency virus (HIV) antibody, hepatitis B surface antigen, hepatitis B e antigen, hepatitis C virus antibody, or Treponema pallidum antibody (tp-trust). 16. Positive in SARS-CoV-2 nucleic acid screening or antibodies (IgG or IgM) screening. 17. Any other situations judged by investigators as not suitable for participating in this study.