Substudy 1  Inclusion Criteria:  Age 18 years - below 65 years A confirmed diagnosis of type 2 DM for ≥ 3 months with stable control (i.e. no change in DM medications in recent 2 months) Written informed consents obtained  Exclusion Criteria:  Known history of confirmed COVID-19 infection Known active sepsis or active malignancy  Known increased infection risk due to underlying immunosuppressed state which includes:  Prior organ or hematopoietic stem cell transplant Neutropenia with absolute neutrophil count (ANC) <500 cells/ul at the time of study inclusion Known HIV infection with CD4 <200 cells/ul at the time of study inclusion On concomitant immunosuppressants or corticosteroid at a dose of prednisolone equivalent dose 10mg or more for more than 3 months Known history or active infective endocarditis On peritoneal dialysis or haemodialysis Documented pregnancy  Substudy 2  Inclusion Criteria:  Age 65 years and above Written informed consents obtained  Exclusion Criteria:  Known history of confirmed COVID-19 infection Known active sepsis or active malignancy  Known increased infection risk due to underlying immunosuppressed state which includes:  Prior organ or hematopoietic stem cell transplant Neutropenia with absolute neutrophil count (ANC) <500 cells/ul at the time of study inclusion Known HIV infection with CD4 <200 cells/ul at the time of study inclusion On concomitant immunosuppressants, chemotherapies or corticosteroid at a dose of prednisolone equivalent dose 10mg or more for more than 3 months Known history or active infective endocarditis On peritoneal dialysis or haemodialysis Known active malignancy Known terminal illness with life expectancy less than 3 months