Inclusion Criteria:

- Eligible participants were those who completed the two-dose primary series of ICV
for 6-15 months

- Voluntarily consented to participate in this trial

- Agreed to take effective contraceptive measures (women of childbearing potential)
from signing the informed consent form to 12 months after booster vaccination.

Exclusion Criteria:

- History of allergy to any vaccine or its excipients;

- Presence of severe, uncontrollable or hospitalized diseases;

- History of major surgery within 3 months prior to enrollment;

- History of Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory
Syndrome (MERS) or COVID-19;

- Congenital or acquired immunodeficiency or autoimmune disease;

- Any acute diseases or acute attacks of chronic diseases within 7 days prior to
enrollment;

- Receipt of any COVID-19 prophylactic medication other than primary series of ICV;

- Long-term receipt (>14 consecutive days) of glucocorticoids or other
immunosuppressive agents within the past 6 months;

- Receipt of biological agents, immunopotentiators or immunosuppressants within the
past 6 months;

- Receipt of blood or blood-related products within 3 months prior to vaccination;

- Administration of antipyretics, painkillers or antiallergics within 24 hours prior
to vaccination;

- Participating or planning to participate in other clinical trials during the study
period;

- Pregnant or lactating females, women of childbearing age of pregnancy test positive;

- Presence of any underlying disease or condition which, in the opinion of the
investigator, may place the subject at unacceptable risk, is unable to meet the
requirements of the protocol, or interfere with the assessment of vaccine response.