Inclusion Criteria:

1. Male or female aged ≥18 years old when signing ICF (the specific age range depends
on the authorized age range by local regulatory authority);

2. Participants who were vaccinated with primary series COVID-19 vaccine and/or
received booster vaccination, and the last dose of COVID-19 vaccine was received
more than 3 months;

3. The participant and/or his/her legal guardian and/or his entrusted person can sign
written ICF, and can fully understand the trial procedure, the risk of participating
in the trial, and other interventions that can be selected if they do not
participate in the trial;

4. The baseline SARS-CoV-2 anti-Spike IgG will be measured at the screening period and
an upper IgG limit may be used to screen the participants. It is aimed to recruit
participants who are susceptible to SARS-CoV-2 infection. The participant with the
IgG level higher than the limit may be excluded from the study. The IgG limit will
be determined based on the average level of IgG in a region, and may not be applied
if the incidence rate of COVID-19 is low;

5. The participant and/or his/her legal guardian and/or his entrusted person have the
ability to read, understand, and fill in record cards;

6. Healthy participants or participants with pre-existing medical conditions who are in
stable condition. The "pre-existing medical conditions" include but not limited to
hypertension, diabetes, Chronic cholecystitis and cholelithiasis, chronic gastritis
that meet the described criteria. A stable medical condition is defined as disease
not requiring significant change in therapy or no need for hospitalization as a
consequence of worsening disease state for at least 3 months prior to enrollment;

7. Fertile men and women of childbearing potential voluntarily agree to take effective
contraceptive measures from signing ICF to 6 months after the last dose of study
vaccination; the pregnancy test results of women of childbearing potential are
negative on screening.

Exclusion Criteria:

1. A positive result of nucleic acid test or rapid antigen test for SARS-CoV-2 during
the screening period;

2. Known history of SARS-CoV-2 infection in past 6 months before the study vaccination;

3. Presence of fever within 3 days before the study vaccination;

4. A history of severe allergic reactions to any vaccines or drugs, such as severe skin
eczema, dyspnea, laryngeal edema, and angioneurotic edema;

5. A medical or family history of seizure, epilepsy, encephalopathy and psychosis;

6. Immunocompromised patients suffering from immunodeficiency diseases, important organ
diseases, immune diseases (including Guillain-Barre Syndrome [GBS], systemic lupus
erythematosus, rheumatoid arthritis, asplenia or splenectomy caused by any
circumstances, and other immune diseases that may have an impact on immune response
in the investigator's opinion), etc.;

7. Long-term use of immunosuppressant therapy or immunomodulatory drugs for >14 days
within the six months prior to enrollment. Whereas short-term (≤14 days) use of
oral, inhaled and topical steroids are allowed;

8. Patients on antituberculosis therapy;

9. Presence of severe or uncontrollable cardiovascular diseases, or severe or
uncontrollable disorders related to endocrine system, blood and lymphatic system,
liver and kidney, respiratory system, metabolic and skeletal systems, or
malignancies (skin basal cell carcinoma and carcinoma in-situ of cervix are
exceptions and will not be excluded), such as severe heart failure, severe pulmonary
heart disease, unstable angina, liver failure, or uremia;

10. Contraindications for intramuscular injection or intravenous blood sampling,
including thrombocytopenia and other blood coagulation disorders;

11. Participants who received any immunoglobulin or blood products in the previous 3
months before enrollment, or plan to receive similar products during the study;

12. Participants who received other investigational drugs within 30 days before the
study vaccination or who intend to participate in another clinical study at any time
during the conduct of this study;

13. Participants who have acute illness, such as acute onset of chronic heart failure,
acute sore throat, hypertensive encephalopathy, acute pneumonia, acute renal
insufficiency, acute cholecystitis;

14. Participants vaccinated with influenza vaccine within 14 days or with other vaccines
within 28 days before the study vaccination;

15. Those who donated blood or had blood loss (≥450 mL) within 3 months before the
vaccination or plan to donate blood during the study period;

16. Those who are pregnant or breast-feeding or plan to be pregnant during the study
period;

17. Those who plan to donate ovum or sperms during the study period;

18. Those who cannot follow the trial procedures, or cannot cooperate to complete the
study due to planned relocation or long-term outing;

19. Those unsuitable for participating in the clinical trial as determined by the
investigator because of other abnormalities that are likely to confuse the study
results, or non-conformance with the maximal benefits of the participants;

20. Those who are tested positive for HIV in terms of serology.