This clinical trial adopts a randomized, double-blind and placebo-controlled design.

A total of 16000 participants are planned to be enrolled, of which, Cohort 1: 15000 participants vaccinated with ≥2 doses of inactivated COVID-19 vaccine for ≥6 months will be randomly administered at ratio of 1:1:1 with 1 dose of LIBP-Rec-Vaccine, BIBP-Rec-Vaccine or placebo intramuscularly to the deltoid muscle of upper arm.

Cohort 2: 1000 participants vaccinated with ≥2 doses of mRNA COVID-19 vaccine for ≥6 months will be randomly administered at ratio of 1:1 with 1 dose of LIBP-Rec-Vaccine or BIBP-Rec-Vaccine intramuscularly to the deltoid muscle of upper arm.

Inclusion Criteria:

• Age range: healthy population aged ≥18;
• Judged by the investigator that the health condition is well after inquiry and physical examination;
• Cohort 1: participants vaccinated with ≥2 doses of inactivated COVID-19 vaccines for ≥6 months since the last dose of vaccination; Cohort 2: participants vaccinated with ≥2 doses of mRNA COVID-19 vaccines for ≥6 months since the last dose of vaccination;
• Be able and willing to complete all prescribed study schedules during the whole study period;
• The participant himself/herself is able and willing to understand study procedures, sign the informed consent form voluntarily after informed consent and comply to requirements of the study protocol.

Exclusion Criteria:

• Symptomatic and suspected COVID 19 infection positive ;
• Urine pregnancy test is positive; Women of childbearing age who have positive urine pregnancy test, who are pregnant, lactating, or women who have planned pregnancy within 6 months;
• Auxiliary temperature before vaccination is ≥37.3℃ (tympanic/forehead temperature ≥37.8℃);
• Previous allergy history of vaccine vaccination (such as acute allergic reaction, urticaria, skin eczema, dyspnea, angioneurotic edema or abdominal pain, etc.) or allergy to known components of COVID-19 vaccine;
• Have a history of hospital-diagnosed thrombocytopenia or other coagulation disorders;
• With known immunological impairment or compromised immunological function diagnosed by the hospital;
• Received whole blood, plasma and immunoglobulin therapy within 1 month;
• Known or suspected of suffering from the following diseases: acute or chronic active respiratory diseases, severe cardiovascular diseases [cardiopulmonary failure, hypertension uncontrollable by drugs (systolic blood pressure ≥ 150 mmHg and/or diastolic blood pressure ≥ 95 mmHg)], acute infection, active phase of chronic disease, liver and kidney diseases, severe diabetes, malignant tumor, infectious skin diseases or severe skin allergy, HIV infection, etc. (Examination report can be provided)
• Received live attenuated vaccine within one month before vaccination;
• Received inactivated vaccine within 14 days before vaccination;
• Other contraindications related to vaccination that investigators believe.