It is a single center, randomized, open-labeled, exploratory clinical study to evaluate the safety and immunogenicity of Recombinant SARS-CoV-2 Fusion Protein bivalent Vaccine V-01-B5 as a second booster in adults aged 18-59 years after vaccinated with 3-dose of inactivated vaccines.

Inclusion Criteria:

• Adults aged 18 -59 years old at time of consent, male or female;
• Normal body temperature;
• Participants who have completed 3-dose regimen of inactive vaccination (CoronaVac) against SARS-CoV-2 wild type in the past 5-9 months;
• Female participants who are not pregnant at the time of enrollment (urine pregnancy test is negative), nor during lactating; and has no birth plan and agree to take effective contraception in 7 months after enrollment; and took effective and acceptable contraceptive methods in the previous 2 weeks before the enrollment;
• Be able and willing to complete the study during the entire study and follow-up period;
• Participants who have the ability to understand the study process, sign the informed consent form voluntarily , and be able to comply with the requirements of the clinical study protocol.

Exclusion Criteria:

• Serious chronic diseases or uncontrolled diseases;
• Uncontrolled neurological disorders, epilepsy;
• Received any inactivated vaccine within 1 week or received any attenuated vaccines within 4 weeks;
• Patients with congenital or acquired immunodeficiency;
• History of severe allergy or be allergic to any components of the test vaccines;
• History of hereditary hemorrhagic tendency or coagulation dysfunction;
• Patients with malignant tumors and other patients have a life expectancy less than 1 year;
• Refuse to sign the informed consent form or inability to complete follow-ups as required by the protocol;
• History of previous COVID-19 infection;
• Pregnant or breastfeeding women, or females of childbearing potential who not agree to or able to take effective and acceptable contraceptive methods during the study;
• Participants who have participated in other clinical trials within 3 months or are participating in other clinical trials;
• Those considered by the investigator as inappropriate to participate in the study.