Inclusion Criteria:

• Completed Informed Consent.
• Age ≥ 18 years old.
• Individual is currently working with a trial participating site where individuals receive healthcare ("healthcare worker") or is associated with the site through emergency services or related healthcare services.
• Able to speak and read English or Spanish.
• At risk for COVID-19 infection through one or more of the following work exposures:
  • in the Intensive care unit; or
  • in the Emergency department; or
  • in Emergency services; or
  • in a COVID-19 hospital unit/ward; or
  • in respiratory services; or
  • in COVID-19 testing location;
  • in inpatient hospital unit/area with potential COVID-19 cases.

Exclusion Criteria:

• Prior diagnosis of COVID-19 infection.
• Participation in another COVID-19 prophylaxis trial within 30 days of consent.
• Respiratory illness with new-onset fever (Temperature > 100°F) or ongoing cough or dyspnea within 14 days.
• Known allergy to HCQ or chloroquine.
• Congenital prolonged QT syndrome.
• Current or planned use of QT prolonging drugs (e.g., procainamide, disopyramide, mexiletine, flecainide, propafenone, amiodarone, sotalol, cimetidine, dronedarone, dofetilide, levofloxacin, ciprofloxacin, moxifloxacin).
• End stage renal disease.
• Pre-existing retinopathy.
• Current or planned use of the following for treatment or prevention of COVID-19 infection:
  • Hydroxychloroquine (study drug) or chloroquine;
  • Azithromycin.
• Known cirrhosis or severe liver disease.
• History of severe skin reactions such as Steven-Johnson syndrome, toxic epidermal necrolysis.
• History of psoriasis or porphyria.
• Ventricular arrhythmias requiring medical treatment.
• Severe coronary artery disease or heart failure/cardiomyopathy with ongoing symptoms.
• Current or planned use of use of anti-seizure drugs.
• History of Glucose-6-phosphate dehydrogenase deficiency.