Clinical Study of SARS-CoV-2 Variant mRNA Vaccine in Healthy Participants

Inclusion Criteria: * Adults aged 18 years and older. * Understand the content of the ICF, and voluntarily sign the ICF (If the participant is unable to sign the ICF on his/her own due to illiteracy, an impartial witness is needed). * Participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. * Female participants of childbearing potential or partners of male participants: voluntarily agree to use effective contraception with their partners prior to the (1st dose of) vaccination and must agree to continue such precautions during the study until 3 months after (full) vaccination.\[Effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices(IUDs), sterilization, abstinence, condoms (for male), diaphragms, cervical caps, etc.\]. * For female participants: without childbearing potential (amenorrhea for at least 1 year or documented surgical sterilization) or have used effective contraception with a negative pregnancy test before (each dose of) vaccination in this study. * On the day of vaccination and 24 hours prior to (each dose of) vaccination, axillary temperatures\<37.3℃/99.1°F. * Healthy participants or participants with mild underlying disease \[in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study\]. * (For group 2 and group 3 only) Participants who have received full primary vaccination of licensed SARS-CoV-2 vaccine (3-8 weeks between 2 doses of COVID-19 inactivated vaccine or 2 doses of COVID-19 mRNA vaccine) and whose last dose was given \>6 mony * (For group 1 only) Not have received any COVID-19 vaccine prior to enrollment. Exclusion Criteria: * Any screening hematology and/or blood biochemistry laboratory value that meets the definition of a ≥Grade 1 abnormality, * (For group 1 only) Confirmed SARS-CoV-2 diagnosis within 1 years before screening visit. * History of Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), or other coronavirus infections. * Receipt of medications intended to treat COVID-19 with 1 year. * History of server adverse reaction associated with a vaccine or drug and/or severe allergic reaction (e.g., anaphylaxis) to any component of the study intervention(s). * SARS-CoV-2 RT-PCR positive nasopharyngeal/oropharyngeal swab specimens at screening. * Positive HIV test at screening. * A history or family history of convulsions, epilepsy, encephalopathy and psychosis. * Malignant tumors in the active phase, malignant tumors not receiving adequate treatment, malignant tumors at potential risk of recurrence during the study period. * Asplenia of functional asplenia, complete or partial splenectomy from any cause. * Individuals who receive treatment with radiotherapy or immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids (if systemic corticosteroids are administered for≥14 days at a dose of ≥20 mg/day of prednisone or equivalent), e.g., for cancer or an autoimmune disease, or planned receipt throughout the study. Inhaled/nebulized, intra-articular, epidural, or topical (skin or eyes) corticosteroids are permitted. * Any other licensed vaccines given within 28 days prior to the investigational vaccination, or planned administration of vaccine(s) within 28 days after (full) vaccination. * Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies, form 60 days before vaccine administration, or receipt of any passive antibody therapy specific to COVID-19, from 90 days before vaccine administration, or planned receipt throughout the study. * Blood donation or blood loss ≥450ml within 1 month prior to enrollment or planned to donate blood during the study period. * Participation in other studies involving study intervention within 28 days prior to study entry, and/or during the study. * Women who are pregnant or breastfeeding. * Participants deemed unsuitable for participation in this study based on the investigator's assessment. * (For group 1 only: Criteria for delay of 2nd dose of vaccination) Fever within 24 hours prior to the 2nd dose of vaccination (axillary body temperature ≥37.3℃/99.1°F). * (For group 1 only: Criteria for delay of 2nd dose of vaccination) During treatment/recovery from illness. * (For group 1 only: Criteria for delay of 2nd dose of vaccination) Other conditions considered by the investigator to be unsuitable for vaccination. * (For group 1 only: Criteria for termination of 2nd dose of vaccination) Participants with a positive urine pregnancy or blood pregnancy test (women of childbearing age only). * (For group 1 only: Criteria for termination of 2nd dose of vaccination) Serious allergic reactions or serious adverse events related to vaccination (as assessed by the investigator) following a previous dose of vaccine. * (For group 1 only: Criteria for termination of 2nd dose of vaccination) Positive result for SARS-CoV-2 (positive RT-PCR test). * (For group 1 only: Criteria for termination of 2nd dose of vaccination) The investigator considers inappropriate for the participants to continue participation in the study.