This is a non-randomized, open-label, externally controlled study to evaluate the safety and immnunogenicity of the Omicron COVID-19 Vaccine (Vero Cell), Inactivated in population aged 18 years old and above with no vaccination history of the COVID-19 vaccine. 200 health subjects will be recruited in this study, including 150 aged 18-59 years old and 50 aged 60 years old and above. All subjects will be received 2 doses of Omicron COVID-19 Vaccine (Vero Cell), Inactivated according to the immunization schedule of 0, 21-28 days. The change in neutralizing antibody level at 28 days after the second dose was used to determine whether to receive a further booster dose for ≥3 months.

The occurrence of adverse events within 28 days and serious adverse events within 6 months after vaccination will be observed. In addition, blood samples will be collected on Day 0 before vaccination,Day 14 after dose 1, before dose 2 and on day 14, 28 and month 3, 6, 9, 12 after dose 2. Serum antibody levels, cellular immune responses will be analyzed.

Inclusion Criteria:

• Healthy subjects aged 18 years old and above.
• By asking for medical history and physical examination, the investigator judged - that the health condition is well.
• Female subjects of childbearing age are not nursing or pregnant at the time of enrolment (negative urine pregnancy test) and have no family planning within the first 12 months after enrolment. Effective contraceptive measures have been taken within 2 weeks before inclusion.
• During the whole follow-up period of the study, be able and willing to complete the whole prescribed study plan.
• With self-ability to understand the study procedures, the informed consent & voluntarily sign an informed consent form and be able to comply with the requirements of the clinical study protocol.

Exclusion Criteria:

• Confirmed or suspected cases of SARS-CoV-2 Infection.
• Has a history of SARS, MERS, SARS-CoV-2 infection (self-report, on-site inquiry).
• Has received COVID-19 vaccine (include mRNA, recombinant protein vaccines, vector vaccines, inactivated vaccines, etc.)
• Axillary body temperature > 37.3 ℃ before vaccination
• Previous severe allergic reactions to vaccination (such as acute allergic reactions, urticaria, dyspnea, angioneurotic edema or abdominal pain) or allergy to known ingredients of inactivated SARS-CoV-2 vaccine have occurred (self-report, on-site inquiry).
• History of hospital-diagnosed thrombocytopenia or other coagulation disorder
• Known immunological impairment or low level with hospital diagnosis
• History of uncontrolled epilepsy, other progressive neurological disorders, or Guillain-Barre syndrome (self-report, on-site inquiry).
• Known or suspected concomitant serious diseases include: respiratory disease, acute infection or active chronic disease, liver and kidney disease, severe diabetes, malignant tumor, infection or allergic skin disease, HIV infection.
• Severe cardiovascular disease (cardiopulmonary failure, uncontrolled hypertension, etc.) diagnosed by the hospital, active chronic respiratory disease
• Live attenuated vaccine is inoculated within 1 month before this vaccination
• other vaccines are inoculated within 14 days before this vaccination.
• be participating in or plan to participate in other vaccine clinical trials during this study.
• Contraindications related to vaccination as considered by other investigators.