- known allergy to (components of) the bcg vaccine or serious reaction to prior bcg administration. - known active tuberculosis or any other active or uncontrolled condition that, in the opinion of the investigator or designee, makes participation unsafe or makes it difficult to collect follow-up data over the study period. - hiv-1 infection - note: if evidence of recent hiv negative test is not available, rapid point-of-care testing will be undertaken as part of screening with a separate informed consent process. - symptoms of respiratory tract infection which, in the opinion of the investigator or designee, is likely to interfere with the objectives of the study. - known medical history of any of the following immunocompromised states: - neutropenia (less than 500 neutrophils/mm3) - lymphopenia (less than 400 lymphocytes/mm3) - solid organ or bone marrow transplantation - primary immunodeficiency - active solid or non-solid malignancy or lymphoma within the prior two years - pregnancy and breastfeeding - current treatment with the following medications: - chemotherapy - anti-cytokine therapies - current treatment with oral or intravenous steroids defined as daily doses of 10mg prednisone or equivalent for longer than 3 months - any experimental, unproven treatment against sars-cov-2 infection or covid-19 including but not limited to chloroquine, hydroxychloroquine, remdesivir, lopinavir/ritonavir and interferon beta-1a.

- known allergy to (components of) the bcg vaccine or serious reaction to prior bcg administration. - known active tuberculosis or any other active or uncontrolled condition that, in the opinion of the investigator or designee, makes participation unsafe or makes it difficult to collect follow-up data over the study period. - hiv-1 infection - note: if evidence of recent hiv negative test is not available, rapid point-of-care testing will be undertaken as part of screening with a separate informed consent process. - symptoms of respiratory tract infection which, in the opinion of the investigator or designee, is likely to interfere with the objectives of the study. - known medical history of any of the following immunocompromised states: - neutropenia (less than 500 neutrophils/mm3) - lymphopenia (less than 400 lymphocytes/mm3) - solid organ or bone marrow transplantation - primary immunodeficiency - active solid or non-solid malignancy or lymphoma within the prior two years - pregnancy and breastfeeding - current treatment with the following medications: - chemotherapy - anti-cytokine therapies - current treatment with oral or intravenous steroids defined as daily doses of 10mg prednisone or equivalent for longer than 3 months - any experimental, unproven treatment against sars-cov-2 infection or covid-19 including but not limited to chloroquine, hydroxychloroquine, remdesivir, lopinavir/ritonavir and interferon beta-1a.