1. hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines 2. contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance \< 10 ml/min 3. already taking chloroquine, hydroxychloroquine or 4-aminoquinolines, or history of these medications within the previous 7 days 4. taking prohibited medications 5. known retinal disease 6. inability to be followed up for the trial period 7. known prolonged qt syndrome (however ecg is not required at baseline) 8. known pregnancy or women who are actively trying to become pregnant 9. prior diagnosis of porphyria 10. previously received any dose of covid-19 vaccine the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: * antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide * antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel * antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin * antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine * psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone * migraine treatment: sumatriptan * antihistamines: astemizole * antiemetics: prochlorperazine, metoclopramide * cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane * other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval

1. hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines 2. contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance \< 10 ml/min 3. already taking chloroquine, hydroxychloroquine or 4-aminoquinolines, or history of these medications within the previous 7 days 4. taking prohibited medications 5. known retinal disease 6. inability to be followed up for the trial period 7. known prolonged qt syndrome (however ecg is not required at baseline) 8. known pregnancy or women who are actively trying to become pregnant 9. prior diagnosis of porphyria 10. previously received any dose of covid-19 vaccine the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: * antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide * antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel * antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin * antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine * psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone * migraine treatment: sumatriptan * antihistamines: astemizole * antiemetics: prochlorperazine, metoclopramide * cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane * other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval

hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance < 10 ml/min already taking chloroquine, hydroxychloroquine or 4-aminoquinolines, or history of these medications within the previous 7 days taking prohibited medications known retinal disease inability to be followed up for the trial period known prolonged qt syndrome (however ecg is not required at baseline) known pregnancy or women who are actively trying to become pregnant prior diagnosis of porphyria previously received any dose of covid-19 vaccine the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone migraine treatment: sumatriptan antihistamines: astemizole antiemetics: prochlorperazine, metoclopramide cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval

hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance < 10 ml/min already taking chloroquine, hydroxychloroquine or 4-aminoquinolines, or history of these medications within the previous 7 days taking prohibited medications known retinal disease inability to be followed up for the trial period known prolonged qt syndrome (however ecg is not required at baseline) known pregnancy or women who are actively trying to become pregnant prior diagnosis of porphyria previously received any dose of covid-19 vaccine the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone migraine treatment: sumatriptan antihistamines: astemizole antiemetics: prochlorperazine, metoclopramide cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval

1. hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines 2. contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance < 10 ml/min 3. already taking chloroquine, hydroxychloroquine or 4-aminoquinolines, or history of these medications within the previous 7 days 4. taking prohibited medications 5. known retinal disease 6. inability to be followed up for the trial period 7. known prolonged qt syndrome (however ecg is not required at baseline) 8. known pregnancy or women who are actively trying to become pregnant 9. prior diagnosis of porphyria 10. previously received any dose of covid-19 vaccine the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: - antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide - antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel - antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin - antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine - psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone - migraine treatment: sumatriptan - antihistamines: astemizole - antiemetics: prochlorperazine, metoclopramide - cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane - other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval

1. hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines 2. contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance < 10 ml/min 3. already taking chloroquine, hydroxychloroquine or 4-aminoquinolines, or history of these medications within the previous 7 days 4. taking prohibited medications 5. known retinal disease 6. inability to be followed up for the trial period 7. known prolonged qt syndrome (however ecg is not required at baseline) 8. known pregnancy or women who are actively trying to become pregnant 9. prior diagnosis of porphyria 10. previously received any dose of covid-19 vaccine the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: - antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide - antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel - antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin - antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine - psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone - migraine treatment: sumatriptan - antihistamines: astemizole - antiemetics: prochlorperazine, metoclopramide - cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane - other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval

1. hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines 2. contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance < 10 ml/min 3. already taking chloroquine, hydroxychloroquine or 4-aminoquinolines 4. taking prohibited medications 5. known retinal disease 6. inability to be followed up for the trial period 7. known prolonged qt syndrome (however ecg is not required at baseline) 8. known pregnancy or women who are actively trying to become pregnant 9. prior diagnosis of porphyria the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: - antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide - antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel - antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin - antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine - psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone - migraine treatment: sumatriptan - antihistamines: astemizole - antiemetics: prochlorperazine, metoclopramide - cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane - other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval

1. hypersensitivity reaction to chloroquine, hydroxychloroquine or 4-aminoquinolines 2. contraindication to taking chloroquine as prophylaxis e.g. known epileptic, known creatinine clearance < 10 ml/min 3. already taking chloroquine, hydroxychloroquine or 4-aminoquinolines 4. taking prohibited medications 5. known retinal disease 6. inability to be followed up for the trial period 7. known prolonged qt syndrome (however ecg is not required at baseline) 8. known pregnancy or women who are actively trying to become pregnant 9. prior diagnosis of porphyria the investigator may consult the physician's guidance documents for any further questions regarding eligibility of potential participants. prohibited medications for the purpose of study enrollment include: - antiarrhythmic medications: digoxin, amiodarone, sotalol, flecainide - antiparasitic/malarial agents: mefloquine, halofantrine, praziquantel - antibiotics: levofloxacin, moxifloxacin, ciprofloxacin, azithromycin, clarithromycin, erythromycin - antifungal drugs: fluconazole, ketoconazole, itraconazole, terfenadine - psychoactive drugs: lithium, quetiapine, chlorpromazine, thioridazine, ziprasidone, haloperidol, droperidol, methadone - migraine treatment: sumatriptan - antihistamines: astemizole - antiemetics: prochlorperazine, metoclopramide - cancer treatments: abiraterone, dabrafenib, dacomitinib, enzalutamide, idelalisib, mitotane - other specific drugs: ciclosporin, conivaptan, agalsidase alfa or beta, mifepristone, stiripentol principai investigators will also be directed to crediblemeds.org to check other agents that may prolong qt interval