1. Aged over 18 years, 2. Received two doses of the new crown inactivated vaccine at least 4 months ago, 3. According to the medical history and physical examination, the researchers judged to be healthy (excluding the following conditions: known or suspected to suffer from more serious diseases at the same time, including: respiratory diseases, acute infections or active chronic diseases, liver and kidney diseases, malignant tumor, infectious disease, allergic skin disease, HIV infection (test report can be provided), 4. Those who have not been abroad in the past 2 months and have experienced outbreaks in villages/communities, who have not been in contact with people infected with the new coronavirus or suspected cases, who are in the non-isolation period, and who have not been infected with the new coronavirus in the same village/community or suspected cases, 5. Patients are willing to complete the entire study follow-up and sign the informed consent.

1. Aged over 18 years, 2. Received two doses of the new crown inactivated vaccine at least 4 months ago, 3. According to the medical history and physical examination, the researchers judged to be healthy (excluding the following conditions: known or suspected to suffer from more serious diseases at the same time, including: respiratory diseases, acute infections or active chronic diseases, liver and kidney diseases, malignant tumor, infectious disease, allergic skin disease, HIV infection (test report can be provided), 4. Those who have not been abroad in the past 2 months and have experienced outbreaks in villages/communities, who have not been in contact with people infected with the new coronavirus or suspected cases, who are in the non-isolation period, and who have not been infected with the new coronavirus in the same village/community or suspected cases, 5. Patients are willing to complete the entire study follow-up and sign the informed consent.

1. Aged >18years, 2. Subjects have inoculated two doses of inactivated Novel Coronavirus Pneumonia vaccine for more than 4 months, 3. According to the medical history and physical examination, the researcher shall judge that the subjects are healthy (subjects with known or suspected diseases exclude: severe respiratory diseases, acute infection or active stage of chronic diseases, liver and kidney diseases, malignant tumors, Infectious diseases, allergic skin disease, HIV infection), 4. In the past two months, the subjects have not been to outland, villages / communities with epidemic situation, and have not been exposed to Novel Coronavirus Pneumonia, 5. The subjects comply with the study and sign the informed consent voluntarily.

1. Aged >18years, 2. Subjects have inoculated two doses of inactivated Novel Coronavirus Pneumonia vaccine for more than 4 months, 3. According to the medical history and physical examination, the researcher shall judge that the subjects are healthy (subjects with known or suspected diseases exclude: severe respiratory diseases, acute infection or active stage of chronic diseases, liver and kidney diseases, malignant tumors, Infectious diseases, allergic skin disease, HIV infection), 4. In the past two months, the subjects have not been to outland, villages / communities with epidemic situation, and have not been exposed to Novel Coronavirus Pneumonia, 5. The subjects comply with the study and sign the informed consent voluntarily.