- known allergy to (components of) the bcg vaccine or serious adverse events to prior bcg administration - known active or latent infection with mycobacterium tuberculosis (m. tuberculosis) or other mycobacterial species - previous m. tuberculosis infection - previous confirmed covid-19 infection - fever (>38 c) within the past 24 hours - suspicion of active viral or bacterial infection - pregnancy - severely immunocompromised subjects (this exclusion category comprises a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) subjects with solid organ transplantation; c) subjects with bone marrow transplantation; d) subjects under chemotherapy; e) subjects with primary immunodeficiency; f) treatment with any anti-cytokine therapies. g) treatment with oral or intravenous steroids defined as daily doses of 10 mg prednisone or equivalent for longer than 3 months) - active solid or non-solid malignancy or lymphoma within the prior two years; - direct involvement in the design or the execution of the bcg-denmark-covid study - employed to the hospital < 22 hours per week - not in possession of a smartphone/tablet.

- known allergy to (components of) the bcg vaccine or serious adverse events to prior bcg administration - known active or latent infection with mycobacterium tuberculosis (m. tuberculosis) or other mycobacterial species - previous m. tuberculosis infection - previous confirmed covid-19 infection - fever (>38 c) within the past 24 hours - suspicion of active viral or bacterial infection - pregnancy - severely immunocompromised subjects (this exclusion category comprises a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) subjects with solid organ transplantation; c) subjects with bone marrow transplantation; d) subjects under chemotherapy; e) subjects with primary immunodeficiency; f) treatment with any anti-cytokine therapies. g) treatment with oral or intravenous steroids defined as daily doses of 10 mg prednisone or equivalent for longer than 3 months) - active solid or non-solid malignancy or lymphoma within the prior two years; - direct involvement in the design or the execution of the bcg-denmark-covid study - employed to the hospital < 22 hours per week - not in possession of a smartphone/tablet.