About 15,000 to 25,000 subjects will be screened. Their information will be collected, venous blood will be sampled, their serum antibody levels will be detected, and the incidence of COVID-19 wil be followed up.

Data of the following will be collected:

1. Demographic data,including Name, Gender, Ethnic groups, ID Card number (age automatically calculated), Height/weight (automatic BMI calculation);
2. Previous disease/surgical history; 3. Previous COVID-19 infections; 4. COVID-19 vaccination history; 5. Infection after this screening; 6. Screening information for COVID-19 antibodies.

Atibody level against SARS-CoV-2 will be test.

Inclusion Criteria:

• The age when signing ICF should be ≥3 year, male or female.
• The Subject and/or guardian or client of both parties are able to sign a written ICF and voluntarily participate in the trial, fully understand the trial procedure, the risks of participating in the study.
• Healthy subjects or subjects with stable underlying diseases. Stable underlying diseases were defined as those who were in stable condition at least 3 months before inclusion in the study, had no significant change in treatment regimen and had not been admitted to hospital due to disease progression.

Exclusion Criteria:

• a history of contraindications for venous blood collection such as thrombocytopenia or other clotting disorders.
• Current severe or uncontrollable cardiovascular disease, endocrine disease, blood and lymphatic system disease, liver and kidney disease, respiratory system disease, metabolic and skeletal system disease, or malignancy.
• If it is not in line with the benefit maximization of the subjects, the investigator determines that it is not suitable to participate in clinical research.

Screening by sampling from natural communities.

Distribution analysis and correlation analysis of antibody will be done and published in academic journals.