- previously (medical history) or currently infected or ill with covid-19 - previous tb disease - fever (>38 c) within the past 24 hours - currently pregnant or breastfeeding or planning on becoming pregnant within 30 days of enrollment - current serious underlying medical conditions including: diabetes mellitus, chronic kidney disease, or any other immunocompromising condition: - known infection by human immunodeficiency virus (hiv) - history of solid organ or bone marrow transplantation - currently under chemotherapy - currently on any anti-cytokine therapy - history of immunodeficiency (including history of anti b cell therapy) - currently taking immunosuppressive drugs - treatment with oral or intravenous steroids, defined as daily doses of 10mg prednisone or equivalent for longer than 3 months - active solid or non-solid malignancy or lymphoma within the past two years - suspicion of active viral or bacterial infection - living with someone hiv+, who is immunocompromised, or is taking an immunosuppressive drug - known allergy to (components of) the bcg vaccine or a serious reaction to prior bcg administration - plan to terminate their employment at the participating health care facility or change duty stations within the next three months - not in possession of a smartphone - current participation in a covid-19 interventional trial

- previously (medical history) or currently infected or ill with covid-19 - previous tb disease - fever (>38 c) within the past 24 hours - currently pregnant or breastfeeding or planning on becoming pregnant within 30 days of enrollment - current serious underlying medical conditions including: diabetes mellitus, chronic kidney disease, or any other immunocompromising condition: - known infection by human immunodeficiency virus (hiv) - history of solid organ or bone marrow transplantation - currently under chemotherapy - currently on any anti-cytokine therapy - history of immunodeficiency (including history of anti b cell therapy) - currently taking immunosuppressive drugs - treatment with oral or intravenous steroids, defined as daily doses of 10mg prednisone or equivalent for longer than 3 months - active solid or non-solid malignancy or lymphoma within the past two years - suspicion of active viral or bacterial infection - living with someone hiv+, who is immunocompromised, or is taking an immunosuppressive drug - known allergy to (components of) the bcg vaccine or a serious reaction to prior bcg administration - plan to terminate their employment at the participating health care facility or change duty stations within the next three months - not in possession of a smartphone - current participation in a covid-19 interventional trial