The phase I/II study is to evaluate the safety and immunogenicity of SARS-COV-2 mRNA Vaccine (RBMRNA-176) at different doses in healthy subjects aged 18 years and older.

Inclusion Criteria:

1. Adults aged 18 years and older, Body Mass Index (BMI) is between 18-30, able to provide legal proof of identity
2. Participants voluntarily agreed to participate in the study and signed an informed consent form
3. The subject has ability to understand the research process and is willing and able to comply with all research proposals and other requirements of the study
4. Axillary temperature ≤37.3°C on the day of injection
5. Negative SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) test, without infective history of severe acute respiratory syndrome (SARS), coronavirus disease 2019 (COVID-19), Middle East Respiratory Syndrome (MERS)
6. Female subjects of childbearing age are not at pregnant period (negative result of pregnancy test) or lactation period
7. Female subjects of childbearing age had taken effective contraceptive measures 1 month before enrollment
8. Female subjects of childbearing age and male subjects agree to use effective contraception for 12 months from the screening visit to the full injection
9. Female subjects of childbearing age and male subjects agree that do not donate eggs (eggs, oocytes) for assisted reproduction (female subjects of childbearing age) or avoid sperm donation (male subjects) from screening period until 12 months after injection

Exclusion Criteria:

1. Chest x - ray is clinically significant abnormal as determined by the investigators
2. The vital signs or examinations are clinically significant abnormal as determined by the investigators prior to randomization
3. A history of severe allergy (including drugs, vaccines, and foods) or to any component of the experimental vaccine, e.g., allergic shock, allergic laryngeal edema, anaphylactoid purpura, dyspnea, and angioedema, etc.
4. Subjects have been diagnosed with a serious disease, congenital malformation or chronic disease (including but not limited to: respiratory disease or chronic bronchitis such as asthma, serious cardiovascular disease, kidney disease, autoimmune disease, thrombocytopenic purpura, thalassemia, malignant tumor, hereditary allergic constitution, etc.) that may interfere with the conduct or completion of the study
5. Diagnosed with diseases may affect immune system function, congenital or acquired immune deficiency or suppression (e.g., tuberculosis, human immunodeficiency virus (HIV)), Hepatitis B, hepatitis C, syphilis infection, uncontrollable autoimmune disease, no spleen or spleen dysfunction
6. Lymph node - related diseases (such as lymphadenitis, lymph node adhesion, lymph node tuberculosis, tumor metastasis, etc.) or skin scars and fistulas at the lymph node site, or lymphadenopathy, tenderness, skin redness and swelling at the lymph node site within 7 days prior to injection
7. History or family history of convulsions, epilepsy, encephalopathy, psychiatry, or history of narcolepsy
8. Within 3 days prior to injection, an acute illness or attack of a chronic disease, or the use of antipyretic analgesic or anti - allergic drugs
9. Subjects have contraindications to intramuscular injection, such as having been diagnosed with thrombocytopenia, any blood clotting disorder or receiving anticoagulant therapy
10. Long-term use of immunopotentiator or immunosuppressant therapy within 6 months prior to the first dose injection (continuous orally or by injection for more than 14 days).
11. Use of any blood or blood - related products (e.g., blood transfusion, use of human albumin, human immunoglobulin, etc.) within 6 months prior to the first dose injection
12. Any blood lost > 400 mL within 28 days prior to the screening visit (e.g., donate blood or component blood, or injured), or plan to donate blood or component blood between the screening visit and 28 days after the last dose injection
13. Previously received any SARS-CoV-2 vaccine or plan to receive other SARS-CoV-2 vaccines
14. Other vaccines have been administered within 4 weeks prior to the first dose injection or other injection schedule (except for emergency injections such as Rabies vaccine and Tetanus vaccine) between the screening period and 28 days after the injection
15. Any abnormal or permanent body art (such as tattoos) at the site of the injection, which the researchers think to interfere with observing local reactions at the site of the injection
16. Female subjects planning to become pregnant or male subjects' partners planning to become pregnant from screening period to 12 months after whole schedule injection
17. Participating in or planning to participate in other clinical trials (drugs or vaccines) within 3 months prior to participating in this study
18. Other circumstances considered by the investigator as inappropriate to participate in the study