sequential immunization of two doses of inactivated covid-19 vaccine (omicron) in vaccinated population aged 18 years and above

Conditions: COVID-19

Summary: this trial adopts a randomized, double-blind and positive control design, it is planned to recruit 1800 healthy participants who have been vaccinated with 2/3 doses of covid-19 inactivated vaccine or mrna vaccine for 3 months. the participants will be divided into two strata according to the types of vaccines administered, including 900 participants of covid-19 inactivated vaccine and 900 participants of mrna vaccine. according to the ratio of 1:1:1, each stratum was randomly assigned to three groups: sequential bibp- covid-19 inactivated vaccine (omicron), wibp-covid-19 inactivated vaccine (omicron) or covid-19 inactivated vaccine (prototype strain). and according to d0, d28 immunization schedule, two doses of corresponding group vaccines are sequentially administered.


Eligibility criteria:
inclusion criteria: * age range: populations aged 18 years and above. * judged by the investigator that the health condition is well after inquiry and physical examination. * vaccinated with 2 doses/3 doses of inactivated covid-19 vaccine or mrna vaccine for ≥ 3 months. * female participants who are not nursing or pregnant at the time of enrolment (negative urine pregnancy test) and have no family planning within the first 7 months after enrollment. 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 is able to comply with the requirements of the clinical study protocol. exclusion criteria: * confirmed cases, suspected cases or asymptomatic cases of covid-19; * with a history of severe acute respiratory syndrome (sars) and middle east respiratory syndrome (mers) (self-report, on-site inquiry); * has vaccinated with one or four doses and above covid-19 vaccine; * axillary temperature ≥37.3℃ (tympanic temperature ≥ 37.6 ℃); * previous allergic reactions to drug or vaccination (such as acute allergic reactions, urticaria, eczema, dyspnea, angioneurotic edema or abdominal pain) or allergy to known components of covid-19 vaccine (self-report, onsite enquiry); * have a history of hospital-diagnosed thrombocytopenia or other coagulation disorders (self-report, onsite enquiry); * with known immunological impairment or immunocompromised diagnosed by the hospital (self-report, onsite enquiry); * have an uncontrolled epilepsy and other progressive neurological diseases or a history of guillain-barre syndrome (self-report, onsite enquiry); * received whole blood, plasma and immunoglobulin therapy within 1 month (self-report, onsite enquiry); * known or suspected severe illness includes: respiratory illness, acute infection or active attacks of chronic illness, liver and kidney disease, severe diabetes mellitus, malignant tumor, infectious or allergic skin disease, human immunodeficiency virus (hiv) infection (self-report, onsite enquiry, provide test report if available); * with hospital-diagnosed serious cardiovascular diseases (cardiopulmonary failure, drug-uncontrolled hypertension (physical examination of systolic blood pressure ≥ 140 mmhg and/or diastolic blood pressure ≥ 90 mmhg), acute attacks of chronic respiratory illness (self-report, onsite enquiry); * received live attenuated vaccines within 1 month before vaccination (self-report, onsite enquiry); * received inactivated vaccines within 14 days before vaccination (self-report, onsite enquiry); * participating or planning to participate in other interventional vaccine clinical trials during this study * other vaccination-related contraindications considered by investigators.