1.Adult subjects (18 years old), no gender limitation, 2.Subjects in good health or stable clinical situation, 3.Subjects who completed two doses of inactivated COVID-19 vaccine 4-8 months ago, 4.Female subjects of childbearing age are not breast-feeding or pregnant (negative blood pregnancy test), and have no family planning in the first 3 months after enrollment. Take effective contraceptive measures within 2 weeks before enrollment, 5.Participant is willing and able to adhere to the procedures specified in this protocol, 6.Participants must provide consent indicating that he or she understands the purpose, procedures and potential risks and benefits of the study, and is willing to participate in the study.

1.Adult subjects (18 years old), no gender limitation, 2.Subjects in good health or stable clinical situation, 3.Subjects who completed two doses of inactivated COVID-19 vaccine 4-8 months ago, 4.Female subjects of childbearing age are not breast-feeding or pregnant (negative blood pregnancy test), and have no family planning in the first 3 months after enrollment. Take effective contraceptive measures within 2 weeks before enrollment, 5.Participant is willing and able to adhere to the procedures specified in this protocol, 6.Participants must provide consent indicating that he or she understands the purpose, procedures and potential risks and benefits of the study, and is willing to participate in the study.