Antibiotics and Vaccine Immune Responses Study

Inclusion Criteria: * 18-35 years old * Provided a signed and dated informed consent form * BCG naïve (Arm 1) and BCG and YF vaccine naïve (Arm 2) * Willing to take short antibiotic course * Willing to undergo a punch biopsy (Arm 1) * Willing to have up to 7 blood samples and 3 stool samples collected over 5-7 months * Not pregnant or intending to get pregnant for the duration of the study (a pregnancy test will be offered to females) Exclusion Criteria: * Previous BCG or YF vaccination * Previous YF infection * Evidence of latent TB infection (LTBI) (assessed through a questionnaire) (IGRA to confirm if needed) * People with contraindications for BCG vaccination: * malignancies involving bone marrow or lymphoid systems, primary or secondary immunodeficiencies, HIV infection * moderate/severe skin disease including eczema, dermatitis or psoriasis * requiring immunosuppressive drugs or other immune modifying drugs e.g. corticosteroids, non-biological immunosuppressants, biological agents (such as monoclonal antibodies against tumour necrosis factor (TNF)-alpha) * People with contraindications to YF vaccination: * History of thymus disease, including myasthenia gravis, thymoma, thymectomy, DiGeorge syndrome, thymic damage from chemoradiotherapy or graft-versus-host disease * YF vaccination is contraindicated in immunocompromised individuals, including individuals who have HIV infection, primary immunodeficiencies (including inherited IFNAR1 deficiency), or are ta…