This clinical trial aimed to gather safety and immunogenicity data in COVID-19 vaccine-experienced healthy adults. The main questions it aims to answer are:

• The neutralizing antibodies levels of bivalent mRNA vaccines RQ3027(Alpha/Beta+Omicron XBB.1.5) and RQ3025(Alpha/Beta+Omicron BA.2/4/5) and monovalent mRNA vaccine RQ3013 against the current SARS-CoV-2 circulating variant.
• The safety profile of RQ3027 and RQ3025 given as a second booster dose to COVID-19 vaccine-experienced participants 18 through 55 years of age.
• Explore the protective efficacy by documenting confirmed COVID-19 cases after vaccination.

Inclusion Criteria:

• Healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study.
• Participants 18 through 55 years of ages.
• Participants who have received at least 3 doses COVID-19 vaccine.
• Participants with the last prior dose being 90 or more days before Visit 1(Day 0) or recovered from COVID-19 at least 28 days.
• Participants able to comply with all scheduled visits, laboratory tests and investigator's instruction.

Exclusion Criteria:

• Women who are pregnant or breastfeeding.
• Enrolling in or planning to participate other interventional clinical study.
• Has received systemic immunoglobulins or blood products within 3 months prior to the day of screening.
• History of anaphylaxis, urticaria, or other significant adverse reaction requiring medical intervention after receipt of a vaccine.
• Bleeding disorder considered a contraindication to intramuscular injection or phlebotomy.
• Continued using anticoagulants such as coumarin and related anticoagulants (i.e., warfarin) or oral anticoagulants (i.e., apixaban, rivaroxaban, dabigatran, and edoxaban).
• Having coronary heart disease, hypertension, diabetes, chronic respiratory diseases, tumors and poorly controlled.
• Immunocompromised or having immunosuppressive therapy.
• Suspected or confirmed alcohol/drug dependence.
• Investigator decide unsuitable factors for participating in clinical trials in the investigator's judgment