* has any bcg vaccine contraindication * fever or generalised skin infection (where feasible, randomisation can be delayed until cleared) * weakened resistance toward infections due to a disease in/of the immune system * receiving medical treatment that affects the immune response or other immunosuppressive therapy in the last year. * these therapies include systemic corticosteroids (≥20 mg for ≥2 weeks), non-biological immunosuppressant (also known as 'dmards'), biological agents (such as monoclonal antibodies against tumour necrosis factor (tnf)-alpha). * people with congenital cellular immunodeficiencies, including specific deficiencies of the interferon-gamma pathway * people with malignancies involving bone marrow or lymphoid systems * people with any serious underlying illness (such as malignancy) * nb: people with cardiovascular disease, hypertension, diabetes, and/or chronic respiratory disease are eligible if not immunocompromised, and if they meet other eligibility criteria * known or suspected hiv infection,even if they are asymptomatic or have normal immune function. * this is because of the risk of disseminated bcg infection * people with active skin disease such as eczema, dermatitis or psoriasis at or near the site of vaccination * a different adjacent site on the upper arm can be chosen if necessary * pregnant * although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women who think they could be pregnant or are planning to become pregnant within the next month. * uk specific: although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women of childbearing potential (wocbp) who think they could be pregnant. * spain specific: if the patient is female, and of childbearing potential, she must have a negative pregnancy test at the time of inclusion and practice a reliable method of birth control for 30 days after receiving the bcg vaccination. * another live vaccine administered in the month prior to randomisation * require another live vaccine to be administered within the month following bcg randomisation * if the other live vaccine can be given on the same day, this exclusion criteria does not apply * known anaphylactic reaction to any of the ingredients present in the bcg vaccine * previous active tb disease * currently receiving long term (more than 1 month) treatment with isoniazid, rifampicin or quinolone as these antibiotics have activity against mycobacterium bovis * previous adverse reaction to bcg vaccine (significant local reaction (abscess) or suppurative lymphadenitis) * bcg vaccine given within the last year * have previously had a sars-cov-2 positive test result (positive pcr on a respiratory sample or a positive sars-cov-2 diagnostic antigen test approved by the local jurisdiction's public health policy) * already part of this trial, recruited at a different site/hospital. * participation in another covid-19 prevention trial * have previously received a covid-19-specific vaccine

* has any bcg vaccine contraindication * fever or generalised skin infection (where feasible, randomisation can be delayed until cleared) * weakened resistance toward infections due to a disease in/of the immune system * receiving medical treatment that affects the immune response or other immunosuppressive therapy in the last year. * these therapies include systemic corticosteroids (≥20 mg for ≥2 weeks), non-biological immunosuppressant (also known as 'dmards'), biological agents (such as monoclonal antibodies against tumour necrosis factor (tnf)-alpha). * people with congenital cellular immunodeficiencies, including specific deficiencies of the interferon-gamma pathway * people with malignancies involving bone marrow or lymphoid systems * people with any serious underlying illness (such as malignancy) * nb: people with cardiovascular disease, hypertension, diabetes, and/or chronic respiratory disease are eligible if not immunocompromised, and if they meet other eligibility criteria * known or suspected hiv infection,even if they are asymptomatic or have normal immune function. * this is because of the risk of disseminated bcg infection * people with active skin disease such as eczema, dermatitis or psoriasis at or near the site of vaccination * a different adjacent site on the upper arm can be chosen if necessary * pregnant * although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women who think they could be pregnant or are planning to become pregnant within the next month. * uk specific: although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women of childbearing potential (wocbp) who think they could be pregnant. * spain specific: if the patient is female, and of childbearing potential, she must have a negative pregnancy test at the time of inclusion and practice a reliable method of birth control for 30 days after receiving the bcg vaccination. * another live vaccine administered in the month prior to randomisation * require another live vaccine to be administered within the month following bcg randomisation * if the other live vaccine can be given on the same day, this exclusion criteria does not apply * known anaphylactic reaction to any of the ingredients present in the bcg vaccine * previous active tb disease * currently receiving long term (more than 1 month) treatment with isoniazid, rifampicin or quinolone as these antibiotics have activity against mycobacterium bovis * previous adverse reaction to bcg vaccine (significant local reaction (abscess) or suppurative lymphadenitis) * bcg vaccine given within the last year * have previously had a sars-cov-2 positive test result (positive pcr on a respiratory sample or a positive sars-cov-2 diagnostic antigen test approved by the local jurisdiction's public health policy) * already part of this trial, recruited at a different site/hospital. * participation in another covid-19 prevention trial * have previously received a covid-19-specific vaccine

- has any bcg vaccine contraindication - fever or generalised skin infection (where feasible, randomisation can be delayed until cleared) - weakened resistance toward infections due to a disease in/of the immune system - receiving medical treatment that affects the immune response or other immunosuppressive therapy in the last year. - these therapies include systemic corticosteroids (≥20 mg for ≥2 weeks), non-biological immunosuppressant (also known as 'dmards'), biological agents (such as monoclonal antibodies against tumour necrosis factor (tnf)-alpha). - people with congenital cellular immunodeficiencies, including specific deficiencies of the interferon-gamma pathway - people with malignancies involving bone marrow or lymphoid systems - people with any serious underlying illness (such as malignancy) - nb: people with cardiovascular disease, hypertension, diabetes, and/or chronic respiratory disease are eligible if not immunocompromised, and if they meet other eligibility criteria - known or suspected hiv infection,even if they are asymptomatic or have normal immune function. - this is because of the risk of disseminated bcg infection - people with active skin disease such as eczema, dermatitis or psoriasis at or near the site of vaccination - a different adjacent site on the upper arm can be chosen if necessary - pregnant - although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women who think they could be pregnant or are planning to become pregnant within the next month. - uk specific: although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women of childbearing potential (wocbp) who think they could be pregnant. - spain specific: if the patient is female, and of childbearing potential, she must have a negative pregnancy test at the time of inclusion and practice a reliable method of birth control for 30 days after receiving the bcg vaccination. - another live vaccine administered in the month prior to randomisation - require another live vaccine to be administered within the month following bcg randomisation - if the other live vaccine can be given on the same day, this exclusion criteria does not apply - known anaphylactic reaction to any of the ingredients present in the bcg vaccine - previous active tb disease - currently receiving long term (more than 1 month) treatment with isoniazid, rifampicin or quinolone as these antibiotics have activity against mycobacterium bovis - previous adverse reaction to bcg vaccine (significant local reaction (abscess) or suppurative lymphadenitis) - bcg vaccine given within the last year - have previously had a sars-cov-2 positive test result (positive pcr on a respiratory sample or a positive sars-cov-2 diagnostic antigen test approved by the local jurisdiction's public health policy) - already part of this trial, recruited at a different site/hospital. - participation in another covid-19 prevention trial - have previously received a covid-19-specific vaccine

- has any bcg vaccine contraindication - fever or generalised skin infection (where feasible, randomisation can be delayed until cleared) - weakened resistance toward infections due to a disease in/of the immune system - receiving medical treatment that affects the immune response or other immunosuppressive therapy in the last year. - these therapies include systemic corticosteroids (≥20 mg for ≥2 weeks), non-biological immunosuppressant (also known as 'dmards'), biological agents (such as monoclonal antibodies against tumour necrosis factor (tnf)-alpha). - people with congenital cellular immunodeficiencies, including specific deficiencies of the interferon-gamma pathway - people with malignancies involving bone marrow or lymphoid systems - people with any serious underlying illness (such as malignancy) - nb: people with cardiovascular disease, hypertension, diabetes, and/or chronic respiratory disease are eligible if not immunocompromised, and if they meet other eligibility criteria - known or suspected hiv infection,even if they are asymptomatic or have normal immune function. - this is because of the risk of disseminated bcg infection - people with active skin disease such as eczema, dermatitis or psoriasis at or near the site of vaccination - a different adjacent site on the upper arm can be chosen if necessary - pregnant - although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women who think they could be pregnant or are planning to become pregnant within the next month. - uk specific: although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women of childbearing potential (wocbp) who think they could be pregnant. - spain specific: if the patient is female, and of childbearing potential, she must have a negative pregnancy test at the time of inclusion and practice a reliable method of birth control for 30 days after receiving the bcg vaccination. - another live vaccine administered in the month prior to randomisation - require another live vaccine to be administered within the month following bcg randomisation - if the other live vaccine can be given on the same day, this exclusion criteria does not apply - known anaphylactic reaction to any of the ingredients present in the bcg vaccine - previous active tb disease - currently receiving long term (more than 1 month) treatment with isoniazid, rifampicin or quinolone as these antibiotics have activity against mycobacterium bovis - previous adverse reaction to bcg vaccine (significant local reaction (abscess) or suppurative lymphadenitis) - bcg vaccine given within the last year - have previously had a sars-cov-2 positive test result (positive pcr on a respiratory sample or a positive sars-cov-2 diagnostic antigen test approved by the local jurisdiction's public health policy) - already part of this trial, recruited at a different site/hospital. - participation in another covid-19 prevention trial - have previously received a covid-19-specific vaccine

- has any bcg vaccine contraindication - fever or generalised skin infection (where feasible, randomisation can be delayed until cleared) - weakened resistance toward infections due to a disease in/of the immune system - receiving medical treatment that affects the immune response or other immunosuppressive therapy in the last year. these therapies include systemic corticosteroids (more than or equal to 20 mg for more than or equal to 2 weeks), non-biological immunosuppressant (also known as 'dmards'), biological agents (such as monoclonal antibodies against tumour necrosis factor (tnf)-alpha). - has a congenital cellular immunodeficiency, including specific deficiencies of the interferon-gamma pathway - has a malignancy involving bone marrow or lymphoid systems - has any serious underlying illness (such as malignancy). please note: people with cardiovascular disease, hypertension, diabetes, and/or chronic respiratory disease are eligible if not immunocompromised - known or suspected hiv infection, even if asymptomatic or has normal immune function. this is because of the risk of disseminated bcg infection - has active skin disease such as eczema, dermatitis or psoriasis at or near the site of vaccination. a different site (other than left arm) can be chosen if necessary - pregnant although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women who think they could be pregnant. - another live vaccine administered in the month prior to randomisation - require another live vaccine to be administered within the month following bcg randomisation if the other live vaccine can be given on the same day, this exclusion criteria does not apply - known anaphylactic reaction to any of the ingredient present in the bcg vaccine - previous active tuberculosis (tb) disease - previous adverse reaction to bcg vaccine (significant local reaction (abscess) or suppurative lymphadenitis) - bcg vaccine given within the last year - has previously had a sars-cov-2 positive test result - already part of this trial, recruited at a different hospital - participation in another covid-19 prevention trial

- has any bcg vaccine contraindication - fever or generalised skin infection (where feasible, randomisation can be delayed until cleared) - weakened resistance toward infections due to a disease in/of the immune system - receiving medical treatment that affects the immune response or other immunosuppressive therapy in the last year. these therapies include systemic corticosteroids (more than or equal to 20 mg for more than or equal to 2 weeks), non-biological immunosuppressant (also known as 'dmards'), biological agents (such as monoclonal antibodies against tumour necrosis factor (tnf)-alpha). - has a congenital cellular immunodeficiency, including specific deficiencies of the interferon-gamma pathway - has a malignancy involving bone marrow or lymphoid systems - has any serious underlying illness (such as malignancy). please note: people with cardiovascular disease, hypertension, diabetes, and/or chronic respiratory disease are eligible if not immunocompromised - known or suspected hiv infection, even if asymptomatic or has normal immune function. this is because of the risk of disseminated bcg infection - has active skin disease such as eczema, dermatitis or psoriasis at or near the site of vaccination. a different site (other than left arm) can be chosen if necessary - pregnant although there is no evidence that bcg vaccination is harmful during pregnancy, it is a contra-indication to bcg vaccination. therefore, we will exclude women who think they could be pregnant. - another live vaccine administered in the month prior to randomisation - require another live vaccine to be administered within the month following bcg randomisation if the other live vaccine can be given on the same day, this exclusion criteria does not apply - known anaphylactic reaction to any of the ingredient present in the bcg vaccine - previous active tuberculosis (tb) disease - previous adverse reaction to bcg vaccine (significant local reaction (abscess) or suppurative lymphadenitis) - bcg vaccine given within the last year - has previously had a sars-cov-2 positive test result - already part of this trial, recruited at a different hospital - participation in another covid-19 prevention trial