- inability to provide informed consent - symptomatic for possible covid-19 at baseline or symptoms highly suggestive of covid-19 experienced since 1st march 2020 - hypersensitivity reaction to hydroxychloroquine, chloroquine or 4-aminoquinolines or any formulation excipients - contraindication to taking hydroxychloroquine as prophylaxis e.g known epilepsy - already taking chloroquine, hydroxychloroquine or 4-aminoquinolines - history of any retinopathy including diabetic retinopathy requiring laser therapy - taking medications which are contra-indicated alongside hcq - digoxin, halofantrine, amiodarone, moxifloxacin, cyclosporin, mefloquine, praziquantel, tamoxifen - known history of prolonged qtc - type i diabetes or insulin-dependent type ii diabetes

- inability to provide informed consent - symptomatic for possible covid-19 at baseline or symptoms highly suggestive of covid-19 experienced since 1st march 2020 - hypersensitivity reaction to hydroxychloroquine, chloroquine or 4-aminoquinolines or any formulation excipients - contraindication to taking hydroxychloroquine as prophylaxis e.g known epilepsy - already taking chloroquine, hydroxychloroquine or 4-aminoquinolines - history of any retinopathy including diabetic retinopathy requiring laser therapy - taking medications which are contra-indicated alongside hcq - digoxin, halofantrine, amiodarone, moxifloxacin, cyclosporin, mefloquine, praziquantel, tamoxifen - known history of prolonged qtc - type i diabetes or insulin-dependent type ii diabetes