Inclusion Criteria:  Aged ≥18 years; Permanent residents of study provinces; Able and willing to provide informed consent to participate in the study; Able and willing to provide nasopharyngeal swab and venous blood sample; Able and willing to complete a questionnaire survey for collecting information on histories of COVID-19 vaccination and disease; Considered as suspected cases of SARS-CoV-2 infections by the physicians in the study clinics according to DR national protocol.  Exclusion Criteria:  -