COVID-19 is a novel coronavirus infection caused by respiratory droplets and contact transmission. With the spread of the epidemic, it has become a serious threat to global public health. China has launched a full range of vaccination including the third dose of homologous and sequential booster immunization. To further improve COVID-19 vaccine immunization strategy, we start the clinic research about sequential Immunization With Recombinant Adenovirus Type-5-vectored COVID-19 Vaccine in Health Adults Based on 3 Doses Inactivated COVID-19 Vaccine in Zhejiang province.

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.