Study on the Antibody Level Against SARS-CoV-2 （COVID-19）in Dazhu County in 2023

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.