Sequential Immunization With Recombinant Adenovirus Type-5-vectored COVID-19 Vaccine in Health Adults Based on 3 Doses Inactivated COVID-19 Vaccine

Inclusion Criteria: 1. Volunteers aged 18 and above at the time of screening; 2. Obtain the informed consent of the volunteers and sign the informed consent; 3. Volunteers are able and willing to comply with the requirements of the clinical trial protocol and complete the 6-month study follow-up; 4. Have received 3 doses of Sinovac/Beijing Biological Novel Coronavirus inactivated vaccine with an interval of 6-9 months. Exclusion Criteria: 1. Patients with history or family history of convulsion, epilepsy, encephalopathy and mental illness; 2. Those who are allergic to any of the components of the study vaccine, have had a severe allergic reaction to the vaccine in the past, a history of allergy or asthma; 3. Serious adverse events related to vaccination occurred after previous vaccination; 4) Positive urine pregnancy test in women during lactation or childbearing age; 5\) Acute febrile disease, infectious disease, SARS history; 6) Axillary body temperature \> 37.0℃; 7) Suffering from serious cardiovascular diseases, such as arrhythmia, conduction block, myocardial infarction, severe hypertension and uncontrolled medication (systolic blood pressure ≥180mmHg and/or diastolic blood pressure ≥110mmHg when measured on site); 8) Patients with serious chronic diseases that are in the advanced stage and cannot be controlled smoothly, such as diabetes and thyroid diseases; 9) Congenital or acquired angioedema/neuroedema; 10) Urticaria 1 year before receiving the test vaccine; 11) No spleen or functional no spleen; 12) Patients with chronic obstructive pulmonary disease, pulmonary fibrosis and other pulmonary abnormalities; 13) History of novel coronavirus infection/illness; 14) Have traveled to medium or high risk areas or left the country in the past 21 days; have a history of novel Coronavirus 2019-epidemiological contact; 15) The researcher made a judgment based on various medical, psychological, social or other conditions that might be contrary to the test protocol or affect the subjects to sign informed consent.