• Hypersensitivity reaction to hydroxychloroquine or 4-aminoquinolines • Contraindication to taking hydroxychloroquine as prophylaxis, e.g. known epileptic, known creatinine clearance < 10 ml/min • Already taking chloroquine, hydroxychloroquine or 4-aminoquinolines • Taking a concomitant medication described in section 8.5 of the master protocol, which cannot be safely stopped known retinal disease • Inability to be followed up for the trial period • Known prolonged QT syndrome (ECG will be required for potential participants who report having a heart condition) • Is enrolled in another clinical trial (however participants will be allowed to participate in observational studies)

• Hypersensitivity reaction to hydroxychloroquine or 4-aminoquinolines • Contraindication to taking hydroxychloroquine as prophylaxis, e.g. known epileptic, known creatinine clearance < 10 ml/min • Already taking chloroquine, hydroxychloroquine or 4-aminoquinolines • Taking a concomitant medication described in section 8.5 of the master protocol, which cannot be safely stopped known retinal disease • Inability to be followed up for the trial period • Known prolonged QT syndrome (ECG will be required for potential participants who report having a heart condition) • Is enrolled in another clinical trial (however participants will be allowed to participate in observational studies)