inclusion criteria: * age above 18 years. * male or female * subjects should have banked admscs in celltex (already passed communicable disease screen tests for hiv, syphilis, hepatitis b and c during banking stage) * must understand and voluntarily sign an informed consent for study participation obtained prior to undergoing any study-specific procedures * highly susceptible to sars-cov-2 infections, such as obesity (bmi ≥ 40), early to middle stage of hypertension (systolic pressure ranging above 140 hg or a diastolic pressure ranging from 90 mm hg), diabetic mellitus hemoglobin a1c \>8%), chronic heart disease (one or more conditions including previously diagnosed as coronary artery disease, chronic heart arrhythmia, cardiomyopathy...) chronic pulmonary disease (copd, fibrosis), chronic liver disease (hepatic impairment, defined as any of alt, ast, ldh or bilirubin \> 2 x the upper limit of normal (uln) range according to local laboratory standards) and kidney diseases (serum creatinine \> 133 mmol/l (1.5 mg/dl). no terminal stages of the above medical conditions. * no previous covid-19 history * sars-cov-2 rt-pcr or equivalent tests negative in respiratory tract specimen * blood test for sars-cov-2 igm and igg negative

inclusion criteria: * age above 18 years. * male or female * subjects should have banked admscs in celltex (already passed communicable disease screen tests for hiv, syphilis, hepatitis b and c during banking stage) * must understand and voluntarily sign an informed consent for study participation obtained prior to undergoing any study-specific procedures * highly susceptible to sars-cov-2 infections, such as obesity (bmi ≥ 40), early to middle stage of hypertension (systolic pressure ranging above 140 hg or a diastolic pressure ranging from 90 mm hg), diabetic mellitus hemoglobin a1c \>8%), chronic heart disease (one or more conditions including previously diagnosed as coronary artery disease, chronic heart arrhythmia, cardiomyopathy...) chronic pulmonary disease (copd, fibrosis), chronic liver disease (hepatic impairment, defined as any of alt, ast, ldh or bilirubin \> 2 x the upper limit of normal (uln) range according to local laboratory standards) and kidney diseases (serum creatinine \> 133 mmol/l (1.5 mg/dl). no terminal stages of the above medical conditions. * no previous covid-19 history * sars-cov-2 rt-pcr or equivalent tests negative in respiratory tract specimen * blood test for sars-cov-2 igm and igg negative

inclusion criteria: - age above 18 years. - male or female - subjects should have banked admscs in celltex (already passed communicable disease screen tests for hiv, syphilis, hepatitis b and c during banking stage) - must understand and voluntarily sign an informed consent for study participation obtained prior to undergoing any study-specific procedures - highly susceptible to sars-cov-2 infections, such as obesity (bmi ≥ 40), early to middle stage of hypertension (systolic pressure ranging above 140 hg or a diastolic pressure ranging from 90 mm hg), diabetic mellitus hemoglobin a1c >8%), chronic heart disease (one or more conditions including previously diagnosed as coronary artery disease, chronic heart arrhythmia, cardiomyopathy…) chronic pulmonary disease (copd, fibrosis), chronic liver disease (hepatic impairment, defined as any of alt, ast, ldh or bilirubin > 2 x the upper limit of normal (uln) range according to local laboratory standards) and kidney diseases (serum creatinine > 133 mmol/l (1.5 mg/dl). no terminal stages of the above medical conditions. - no previous covid-19 history - sars-cov-2 rt-pcr or equivalent tests negative in respiratory tract specimen - blood test for sars-cov-2 igm and igg negative

inclusion criteria: - age above 18 years. - male or female - subjects should have banked admscs in celltex (already passed communicable disease screen tests for hiv, syphilis, hepatitis b and c during banking stage) - must understand and voluntarily sign an informed consent for study participation obtained prior to undergoing any study-specific procedures - highly susceptible to sars-cov-2 infections, such as obesity (bmi ≥ 40), early to middle stage of hypertension (systolic pressure ranging above 140 hg or a diastolic pressure ranging from 90 mm hg), diabetic mellitus hemoglobin a1c >8%), chronic heart disease (one or more conditions including previously diagnosed as coronary artery disease, chronic heart arrhythmia, cardiomyopathy…) chronic pulmonary disease (copd, fibrosis), chronic liver disease (hepatic impairment, defined as any of alt, ast, ldh or bilirubin > 2 x the upper limit of normal (uln) range according to local laboratory standards) and kidney diseases (serum creatinine > 133 mmol/l (1.5 mg/dl). no terminal stages of the above medical conditions. - no previous covid-19 history - sars-cov-2 rt-pcr or equivalent tests negative in respiratory tract specimen - blood test for sars-cov-2 igm and igg negative