Study on Sequential Immunization of Inactivated COVID-19 Vaccine and Recombinant COVID-19 Vaccine (Ad5 Vector) in Elderly Adults

Inclusion criteria

• Health subjects aged 60 and above, who have been completed two-dose regimen of inactive SARS-CoV-2 vaccine in the past 3-6 months, or received one dose of inactive SARS-CoV-2 vaccine in the past 1-3 months.
• The subject can provide with informed consent and sign informed consent form (ICF).
• The subjects are able to and willing to comply with the requirements of the clinical trial program and could complete the 6-month follow-up of the study.
• Axillary temperature ≤ 37.0#.
• Individuals who are in good health condition at the time of entry into the trial as determined by medical history, physical examination and clinical judgment of the investigator and meet the requirements of immunization

Exclusion criteria

• have the medical history or family history of convulsion, epilepsy,encephalopathy and psychosis.
• be allergic to any component of the research vaccines, or used to have a history of hypersensitivity or serious reactions to vaccination.
• women with positive urine pregnancy test, pregnant or breast-feeding, or have a pregnancy plan within six months.
• have acute febrile diseases and infectious diseases.
• have severe chronic diseases or condition in progress cannot be controlled.
• congenital or acquired angioedema / neuroedema
• have the history of urticaria 1 year before receiving the investigational vaccine.
• have asplenia or functional asplenia.
• have thrombocytopenia or other coagulation disorders (which may cause contraindications for intramuscular injection).
• have needle sickness.
• have the history of immunosuppressive therapy, anti-allergy therapy,cytotoxic therapy or inhaled corticosteroids (excluding corticosteroidspray therapy for allergic rhinitis, and acute corticosteroid therapy without dermatitis) over the past 6 months.
• have received blood products within 4 months before injection of investigational vaccines.
• under anti-tuberculosis treatment.
• not be able to follow the protocol, or not be able to understand the informed consent according to the researcher's judgment, due to variousmedical, psychological, social or other conditions.