inclusion criteria: written informed consent male or female age more than or equal to 50 years based on the precise date of birth. female participants are allowed on the premise that they are post-menopausal. history of at least one of the following: coronary heart disease; chronic obstructive pulmonary disease; charlson's comorbidity index (cci) more than 3 negative serum testing for immunoglobulin g and m against sars-cov-2 skin tuberculin test diameter less than 10mm

inclusion criteria: written informed consent male or female age more than or equal to 50 years based on the precise date of birth. female participants are allowed on the premise that they are post-menopausal. history of at least one of the following: coronary heart disease; chronic obstructive pulmonary disease; charlson's comorbidity index (cci) more than 3 negative serum testing for immunoglobulin g and m against sars-cov-2 skin tuberculin test diameter less than 10mm

inclusion criteria: 1. written informed consent 2. male or female 3. age more than or equal to 50 years based on the precise date of birth. female participants are allowed on the premise that they are post-menopausal. 4. history of at least one of the following: 1. coronary heart disease; 2. chronic obstructive pulmonary disease; 3. charlson's comorbidity index (cci) more than 3 5. negative serum testing for immunoglobulin g and m against sars-cov-2 6. skin tuberculin test diameter less than 10mm

inclusion criteria: 1. written informed consent 2. male or female 3. age more than or equal to 50 years based on the precise date of birth. female participants are allowed on the premise that they are post-menopausal. 4. history of at least one of the following: 1. coronary heart disease; 2. chronic obstructive pulmonary disease; 3. charlson's comorbidity index (cci) more than 3 5. negative serum testing for immunoglobulin g and m against sars-cov-2 6. skin tuberculin test diameter less than 10mm