* known allergy to (components of) the bcg vaccine or serious adverse events to prior bcg administration * known active or latent mycobacterium tuberculosis or with another mycobacterial species. a history with- or a suspicion of m. tuberculosis infection. * fever (\>38 c) within the past 24 hours * pregnancy * suspicion of active viral or bacterial infection * vaccination in the past 4 weeks or expected vaccination during the study period, independent of the type of vaccination. * severely immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) neutropenic subjects with less than 500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) severe lymphopenia with less than 400 lymphocytes/mm3; h) treatment with any anti-cytokine therapies. i) treatment with oral or intravenous steroids defined as daily doses of 10mg prednisone or equivalent for longer than 3 months, or probable use of oral or intravenous steroids in the following four weeks * active solid or non-solid malignancy or lymphoma within the prior two years * direct involvement in the design or the execution of the bcg-corona study * expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) * employed to the hospital \< 22 hours per week * not in possession of a smartphone

* known allergy to (components of) the bcg vaccine or serious adverse events to prior bcg administration * known active or latent mycobacterium tuberculosis or with another mycobacterial species. a history with- or a suspicion of m. tuberculosis infection. * fever (\>38 c) within the past 24 hours * pregnancy * suspicion of active viral or bacterial infection * vaccination in the past 4 weeks or expected vaccination during the study period, independent of the type of vaccination. * severely immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) neutropenic subjects with less than 500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) severe lymphopenia with less than 400 lymphocytes/mm3; h) treatment with any anti-cytokine therapies. i) treatment with oral or intravenous steroids defined as daily doses of 10mg prednisone or equivalent for longer than 3 months, or probable use of oral or intravenous steroids in the following four weeks * active solid or non-solid malignancy or lymphoma within the prior two years * direct involvement in the design or the execution of the bcg-corona study * expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) * employed to the hospital \< 22 hours per week * not in possession of a smartphone

- known allergy to (components of) the bcg vaccine or serious adverse events to prior bcg administration - known active or latent mycobacterium tuberculosis or with another mycobacterial species. a history with- or a suspicion of m. tuberculosis infection. - fever (>38 c) within the past 24 hours - pregnancy - suspicion of active viral or bacterial infection - vaccination in the past 4 weeks or expected vaccination during the study period, independent of the type of vaccination. - severely immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) neutropenic subjects with less than 500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) severe lymphopenia with less than 400 lymphocytes/mm3; h) treatment with any anti-cytokine therapies. i) treatment with oral or intravenous steroids defined as daily doses of 10mg prednisone or equivalent for longer than 3 months, or probable use of oral or intravenous steroids in the following four weeks - active solid or non-solid malignancy or lymphoma within the prior two years - direct involvement in the design or the execution of the bcg-corona study - expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) - employed to the hospital < 22 hours per week - not in possession of a smartphone

- known allergy to (components of) the bcg vaccine or serious adverse events to prior bcg administration - known active or latent mycobacterium tuberculosis or with another mycobacterial species. a history with- or a suspicion of m. tuberculosis infection. - fever (>38 c) within the past 24 hours - pregnancy - suspicion of active viral or bacterial infection - vaccination in the past 4 weeks or expected vaccination during the study period, independent of the type of vaccination. - severely immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) neutropenic subjects with less than 500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) severe lymphopenia with less than 400 lymphocytes/mm3; h) treatment with any anti-cytokine therapies. i) treatment with oral or intravenous steroids defined as daily doses of 10mg prednisone or equivalent for longer than 3 months, or probable use of oral or intravenous steroids in the following four weeks - active solid or non-solid malignancy or lymphoma within the prior two years - direct involvement in the design or the execution of the bcg-corona study - expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) - employed to the hospital < 22 hours per week - not in possession of a smartphone