Inclusion Criteria:

1. Axillary temperature ≤37.0 ℃.

2. aged 18 years and above, after 3, 4, 5, or 6 months since finished two doses
schedule of CoronaVac or BBIBP-CorV, or one does CoronaVac and one does BBIBP-CorV.

3. Proven legal identity, could come each visit.

4. Participants should understand the contents of the informed consent form, the
vaccine in this trial, voluntarily sign the informed consent form.

Exclusion Criteria:

1. Persons with a clear history of SARS-CoV-2 infection.

2. Using blood products after basic immunization or receiving immunosuppressive
therapy.

3. Participants who have a positive pregnancy test, or are breastfeeding, or plan to
become pregnant, or plan to donate sperm or eggs from the screening to 6 months
after vaccination.

4. Allergic to the active substance in the vaccine, any inactive substance or substance
used in the preparation process (aluminum hydroxide, glycine);

5. History of abnormal clinical manifestations and serious diseases to be excluded,
including but not limited to nervous system, cardiovascular system, blood and
lymphatic system, immune system, kidney, liver, gastrointestinal tract, respiratory
system, metabolism, bones and other system diseases, and a history of malignant
tumors.

6. Diseases beyond drug control, such as high blood pressure, diabetes, asthma.

7. Those who developed acute disease within 2 weeks, or had symptoms of fever or upper
respiratory tract infection within 7 days.

8. Immunization with any vaccine within 14 days.

9. Any other situations judged by investigators as not suitable for participating in
this study.