* fever (\>38 ºc) within the past 24 hours * suspicion of current active viral or bacterial infection; the requirement to finish an antibiotic course upon discharge is not an exclusion criterion when the infection is controlled in the opinion of the attending physician * vaccination with live vaccine in the past four weeks or planned vaccination with live vaccine during the next four weeks * severely immunocompromised participants. this exclusion category comprises: 1. known infection by the human immunodeficiency virus (hiv-1); 2. neutropenic with less than 500 neutrophils/mm3; 3. solid organ transplantation; 4. bone marrow transplantation; 5. hematological malignancy; 6. chemo-, radio- or immunotherapy for solid organ malignancy in the past 6 months; 7. primary immunodeficiency; 8. severe lymphopenia with less than 400 lymphocytes/mm3; 9. treatment with any immunosuppressant drugs such as anti-cytokine therapies, and treatment with oral or intravenous steroids defined as daily doses of \>10 mg/day or a cumulative dose of \>700 mg prednisone or equivalent for other corticosteroids, or probable use of oral or intravenous steroids in the following four weeks * known history of a positive mantoux or active tb; prior bcg vaccination is not an exclusion criterion. * born in a country with high incidence of tb; a list of non-eligible countries will be created by the trial steering committee prior to the first enrolment. * active participation in another research study that involves bcg administration * history of documented covid-19 (self-reported by the participant: either confirmed by a microbiological test or with clinical diagnosis during hospitalization) * not able to perform the study procedures as judged by the attending physician * legally incapacitated or unwilling to provide informed consent

* fever (\>38 ºc) within the past 24 hours * suspicion of current active viral or bacterial infection; the requirement to finish an antibiotic course upon discharge is not an exclusion criterion when the infection is controlled in the opinion of the attending physician * vaccination with live vaccine in the past four weeks or planned vaccination with live vaccine during the next four weeks * severely immunocompromised participants. this exclusion category comprises: 1. known infection by the human immunodeficiency virus (hiv-1); 2. neutropenic with less than 500 neutrophils/mm3; 3. solid organ transplantation; 4. bone marrow transplantation; 5. hematological malignancy; 6. chemo-, radio- or immunotherapy for solid organ malignancy in the past 6 months; 7. primary immunodeficiency; 8. severe lymphopenia with less than 400 lymphocytes/mm3; 9. treatment with any immunosuppressant drugs such as anti-cytokine therapies, and treatment with oral or intravenous steroids defined as daily doses of \>10 mg/day or a cumulative dose of \>700 mg prednisone or equivalent for other corticosteroids, or probable use of oral or intravenous steroids in the following four weeks * known history of a positive mantoux or active tb; prior bcg vaccination is not an exclusion criterion. * born in a country with high incidence of tb; a list of non-eligible countries will be created by the trial steering committee prior to the first enrolment. * active participation in another research study that involves bcg administration * history of documented covid-19 (self-reported by the participant: either confirmed by a microbiological test or with clinical diagnosis during hospitalization) * not able to perform the study procedures as judged by the attending physician * legally incapacitated or unwilling to provide informed consent

fever (>38 ºc) within the past 24 hours suspicion of current active viral or bacterial infection; the requirement to finish an antibiotic course upon discharge is not an exclusion criterion when the infection is controlled in the opinion of the attending physician vaccination with live vaccine in the past four weeks or planned vaccination with live vaccine during the next four weeks severely immunocompromised participants. this exclusion category comprises: known infection by the human immunodeficiency virus (hiv-1); neutropenic with less than 500 neutrophils/mm3; solid organ transplantation; bone marrow transplantation; hematological malignancy; chemo-, radio- or immunotherapy for solid organ malignancy in the past 6 months; primary immunodeficiency; severe lymphopenia with less than 400 lymphocytes/mm3; treatment with any immunosuppressant drugs such as anti-cytokine therapies, and treatment with oral or intravenous steroids defined as daily doses of >10 mg/day or a cumulative dose of >700 mg prednisone or equivalent for other corticosteroids, or probable use of oral or intravenous steroids in the following four weeks known history of a positive mantoux or active tb; prior bcg vaccination is not an exclusion criterion. born in a country with high incidence of tb; a list of non-eligible countries will be created by the trial steering committee prior to the first enrolment. active participation in another research study that involves bcg administration history of documented covid-19 (self-reported by the participant: either confirmed by a microbiological test or with clinical diagnosis during hospitalization) not able to perform the study procedures as judged by the attending physician legally incapacitated or unwilling to provide informed consent

fever (>38 ºc) within the past 24 hours suspicion of current active viral or bacterial infection; the requirement to finish an antibiotic course upon discharge is not an exclusion criterion when the infection is controlled in the opinion of the attending physician vaccination with live vaccine in the past four weeks or planned vaccination with live vaccine during the next four weeks severely immunocompromised participants. this exclusion category comprises: known infection by the human immunodeficiency virus (hiv-1); neutropenic with less than 500 neutrophils/mm3; solid organ transplantation; bone marrow transplantation; hematological malignancy; chemo-, radio- or immunotherapy for solid organ malignancy in the past 6 months; primary immunodeficiency; severe lymphopenia with less than 400 lymphocytes/mm3; treatment with any immunosuppressant drugs such as anti-cytokine therapies, and treatment with oral or intravenous steroids defined as daily doses of >10 mg/day or a cumulative dose of >700 mg prednisone or equivalent for other corticosteroids, or probable use of oral or intravenous steroids in the following four weeks known history of a positive mantoux or active tb; prior bcg vaccination is not an exclusion criterion. born in a country with high incidence of tb; a list of non-eligible countries will be created by the trial steering committee prior to the first enrolment. active participation in another research study that involves bcg administration history of documented covid-19 (self-reported by the participant: either confirmed by a microbiological test or with clinical diagnosis during hospitalization) not able to perform the study procedures as judged by the attending physician legally incapacitated or unwilling to provide informed consent

- fever (>38 ºc) within the past 24 hours - suspicion of current active viral or bacterial infection; the requirement to finish an antibiotic course upon discharge is not an exclusion criterion when the infection is controlled in the opinion of the attending physician - vaccination with live vaccine in the past four weeks or planned vaccination with live vaccine during the next four weeks - severely immunocompromised participants. this exclusion category comprises: 1. known infection by the human immunodeficiency virus (hiv-1); 2. neutropenic with less than 500 neutrophils/mm3; 3. solid organ transplantation; 4. bone marrow transplantation; 5. hematological malignancy; 6. chemo-, radio- or immunotherapy for solid organ malignancy in the past 6 months; 7. primary immunodeficiency; 8. severe lymphopenia with less than 400 lymphocytes/mm3; 9. treatment with any immunosuppressant drugs such as anti-cytokine therapies, and treatment with oral or intravenous steroids defined as daily doses of >10 mg/day or a cumulative dose of >700 mg prednisone or equivalent for other corticosteroids, or probable use of oral or intravenous steroids in the following four weeks - known history of a positive mantoux or active tb; prior bcg vaccination is not an exclusion criterion. - born in a country with high incidence of tb; a list of non-eligible countries will be created by the trial steering committee prior to the first enrolment. - active participation in another research study that involves bcg administration - history of documented covid-19 (self-reported by the participant: either confirmed by a microbiological test or with clinical diagnosis during hospitalization) - not able to perform the study procedures as judged by the attending physician - legally incapacitated or unwilling to provide informed consent

- fever (>38 ºc) within the past 24 hours - suspicion of current active viral or bacterial infection; the requirement to finish an antibiotic course upon discharge is not an exclusion criterion when the infection is controlled in the opinion of the attending physician - vaccination with live vaccine in the past four weeks or planned vaccination with live vaccine during the next four weeks - severely immunocompromised participants. this exclusion category comprises: 1. known infection by the human immunodeficiency virus (hiv-1); 2. neutropenic with less than 500 neutrophils/mm3; 3. solid organ transplantation; 4. bone marrow transplantation; 5. hematological malignancy; 6. chemo-, radio- or immunotherapy for solid organ malignancy in the past 6 months; 7. primary immunodeficiency; 8. severe lymphopenia with less than 400 lymphocytes/mm3; 9. treatment with any immunosuppressant drugs such as anti-cytokine therapies, and treatment with oral or intravenous steroids defined as daily doses of >10 mg/day or a cumulative dose of >700 mg prednisone or equivalent for other corticosteroids, or probable use of oral or intravenous steroids in the following four weeks - known history of a positive mantoux or active tb; prior bcg vaccination is not an exclusion criterion. - born in a country with high incidence of tb; a list of non-eligible countries will be created by the trial steering committee prior to the first enrolment. - active participation in another research study that involves bcg administration - history of documented covid-19 (self-reported by the participant: either confirmed by a microbiological test or with clinical diagnosis during hospitalization) - not able to perform the study procedures as judged by the attending physician - legally incapacitated or unwilling to provide informed consent