1. Study participant is willing to provide informed consent 2. Be aged 18-70 years at the time of consent and in good overall health 3. Health care worker at high risk of COVID-19 exposure including doctors, nurses and other allied health care workers (such as physiotherapist, radiographer, speech/occupational therapists, personal services assistants, dentist/dental nurse/dental hygienists, aged care workers, optometrist, in general practice or other health care services or paramedic (ambulance) in the following settings: • Emergency department • COVID-19 management teams: Outpatient Clinic • Inpatient Ward • Intensive care unit/ High Dependency Unit (HDU) /Operating Theatre/ Recovery • Groups exposed to aerosol generating procedures: eg. anaesthetics/intubation teams • Dental Services • Aged Care Homes • Optometry Services • Otolaryngology Services (ENT) • Occupational & Speech Therapy • Physiotherapy • Paramedicine/Ambulatory • Radiology • General Practice • Other Health Care Services Worker 4. Anticipated to be performing clinical duties as a front-line health care worker during the trial period 5. Willing to adhere to study procedures including daily use of mobile electronic portal to report outcomes and adverse events 6. Willing to take drug/placebo as directed and to not take additional hydroxychloroquine or chloroquine during the trial period 7. Willing to provide COVID-19 test results and permission to use the COVID-19 registry at the end of the study to confirm COVID-19 status 8. Willing to report hospitalisations to the study nurse and to have review of medical records and receive follow-up phone calls to determine outcomes of hospitalisations

1. Study participant is willing to provide informed consent 2. Be aged 18-70 years at the time of consent and in good overall health 3. Health care worker at high risk of COVID-19 exposure including doctors, nurses and other allied health care workers (such as physiotherapist, radiographer, speech/occupational therapists, personal services assistants, dentist/dental nurse/dental hygienists, aged care workers, optometrist, in general practice or other health care services or paramedic (ambulance) in the following settings: • Emergency department • COVID-19 management teams: Outpatient Clinic • Inpatient Ward • Intensive care unit/ High Dependency Unit (HDU) /Operating Theatre/ Recovery • Groups exposed to aerosol generating procedures: eg. anaesthetics/intubation teams • Dental Services • Aged Care Homes • Optometry Services • Otolaryngology Services (ENT) • Occupational & Speech Therapy • Physiotherapy • Paramedicine/Ambulatory • Radiology • General Practice • Other Health Care Services Worker 4. Anticipated to be performing clinical duties as a front-line health care worker during the trial period 5. Willing to adhere to study procedures including daily use of mobile electronic portal to report outcomes and adverse events 6. Willing to take drug/placebo as directed and to not take additional hydroxychloroquine or chloroquine during the trial period 7. Willing to provide COVID-19 test results and permission to use the COVID-19 registry at the end of the study to confirm COVID-19 status 8. Willing to report hospitalisations to the study nurse and to have review of medical records and receive follow-up phone calls to determine outcomes of hospitalisations

1. Study participant is willing to provide informed consent 2. Be aged 18-70 years at the time of consent 3. High risk exposure health care worker including doctors, nurses, allied health workers in the following settings: • Emergency department • COVID-19 management teams: fever clinic and COVID-19 hospital ward • Intensive care unit • Groups exposed to aerosol generating procedures: eg. intubation teams, dentists, ophthalmologists 4. Anticipated to be performing clinical duties as a front-line health care worker during the trial period 5. Willing to adhere to study procedures including daily use of mobile electronic portal to report outcomes and adverse events 6. Willing to take drug/placebo as directed and to not take additional hydroxychloroquine or chloroquine during the trial period 7. Willing to provide COVID-19 test results and permission to use the COVID-19 registry at the end of the study to confirm COVID-19 status 8. Willing to report hospitalisations to the study nurse and to have review of medical records and receive follow-up phone calls to determine outcomes of hospitalisations

1. Study participant is willing to provide informed consent 2. Be aged 18-70 years at the time of consent 3. High risk exposure health care worker including doctors, nurses, allied health workers in the following settings: • Emergency department • COVID-19 management teams: fever clinic and COVID-19 hospital ward • Intensive care unit • Groups exposed to aerosol generating procedures: eg. intubation teams, dentists, ophthalmologists 4. Anticipated to be performing clinical duties as a front-line health care worker during the trial period 5. Willing to adhere to study procedures including daily use of mobile electronic portal to report outcomes and adverse events 6. Willing to take drug/placebo as directed and to not take additional hydroxychloroquine or chloroquine during the trial period 7. Willing to provide COVID-19 test results and permission to use the COVID-19 registry at the end of the study to confirm COVID-19 status 8. Willing to report hospitalisations to the study nurse and to have review of medical records and receive follow-up phone calls to determine outcomes of hospitalisations