* 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 * age \> 75 years * pregnancy or planning pregnancy within 30 days of study enrollment * breastfeeding * suspicion of active viral or bacterial infection * any immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) subjects with known neutropenic with less than 1500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) known 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 * living with someone who is immunosuppressed or taking immunosuppressive drugs * previous documented infection with covid19 * active solid or non-solid malignancy or lymphoma within the prior two years * direct involvement in the design or the execution of the study * expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) * not in possession of a smartphone * inability to keep the vaccine site covered in the case of a draining pustule.

* 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 * age \> 75 years * pregnancy or planning pregnancy within 30 days of study enrollment * breastfeeding * suspicion of active viral or bacterial infection * any immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) subjects with known neutropenic with less than 1500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) known 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 * living with someone who is immunosuppressed or taking immunosuppressive drugs * previous documented infection with covid19 * active solid or non-solid malignancy or lymphoma within the prior two years * direct involvement in the design or the execution of the study * expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) * not in possession of a smartphone * inability to keep the vaccine site covered in the case of a draining pustule.

- 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 - age > 75 years - pregnancy or planning pregnancy within 30 days of study enrollment - breastfeeding - suspicion of active viral or bacterial infection - any immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) subjects with known neutropenic with less than 1500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) known 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 - living with someone who is immunosuppressed or taking immunosuppressive drugs - previous documented infection with covid19 - active solid or non-solid malignancy or lymphoma within the prior two years - direct involvement in the design or the execution of the study - expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) - not in possession of a smartphone - inability to keep the vaccine site covered in the case of a draining pustule.

- 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 - age > 75 years - pregnancy or planning pregnancy within 30 days of study enrollment - breastfeeding - suspicion of active viral or bacterial infection - any immunocompromised subjects. this exclusion category comprises: a) subjects with known infection by the human immunodeficiency virus (hiv-1); b) subjects with known neutropenic with less than 1500 neutrophils/mm3; c) subjects with solid organ transplantation; d) subjects with bone marrow transplantation; e) subjects under chemotherapy; f) subjects with primary immunodeficiency; g) known 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 - living with someone who is immunosuppressed or taking immunosuppressive drugs - previous documented infection with covid19 - active solid or non-solid malignancy or lymphoma within the prior two years - direct involvement in the design or the execution of the study - expected absence from work of ≥4 of the following 12 weeks due to any reason (holidays, maternity leave, retirement, planned surgery etc) - not in possession of a smartphone - inability to keep the vaccine site covered in the case of a draining pustule.