Inclusion Criteria Cohort A: - ≥ 18 years old - Employee of healthcare organization in South Dakota or Sanford Health employee in any location and with exposure to a person with COVID-19 within the last 5 days - Occupational exposure as determined by the participant's employee health department (i.e. not wearing the proper Personal Protective Equipment (PPE)) - Criteria according to Center for Disease Control (CDC) guidelines - Community exposure (within 6 feet for at least 15 minutes) - No current symptoms attributable to COVID-19, per HCW report (fever, cough, difficulty breathing, sore throat) - No prior COVID-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) - Ability to provide informed consent Inclusion Criteria - Cohort B - ≥ 18 years old - High-risk person who had close contact (i.e. within 6 feet for at least 15 minutes) with a COVID-19 positive person within the last 5 days and is a South Dakota resident or high-risk person with close household contact of a COVID-19 positive Sanford employee - High-risk person defined by: - Age 18-44 with 2 or more comorbidities listed below - Age 45-79 with any comorbid condition listed below - Age 80 and above (regardless of comorbid conditions) - Co-morbid list - Congestive Heart Failure (CHF) - Chronic lung disease (Includes any of the following: asthma, chronic obstructive pulmonary disease, emphysema) - Solid organ transplant or immunosuppression (Defined as an outpatient prescription of greater than 10 mg/day of prednisone or equivalent, use of chemotherapy, or use of immunosuppressive agents for solid organ transplant or for an autoimmune disease.) - Chronic Kidney Disease or End Stage Renal Disease - Diabetes mellitus - Cardiovascular disease/Hypertension - Smoking/Vaping (currently using or history of using in the past 1 year) - Obesity (calculated by height and weight per participant report) - Hyperlipidemia - No current symptoms attributable to COVID-19 - No prior COVID-19 positive diagnosis (eligible if previous testing is negative and meets all other inclusion and exclusion) - Ability to provide informed consent - Confirmed review of concomitant medications (with emphasis on cardiac medications)

Cohort A & B: - Known allergy to hydroxychloroquine or quinine - Known history of long QT syndrome - Known history of arrhythmia or dysrhythmia - Known current QTc >500 ms - Known G6PD deficiency - Known history of hypoglycemia - Pregnant or Nursing by patient history - Use of any of the following concomitant medications: See Appendix D for Exclusion medication list - Concurrent diagnosis of dermatitis, porphyria, or psoriasis - History of chronic liver disease, including cirrhosis and/or diagnosis of hepatitis (infectious, idiopathic, or immune) - History of chronic kidney disease - Pre-existing retinopathy - Already taking hydroxychloroquine - Any condition or medication in the opinion of the investigator that would prohibit the use of hydroxychloroquine - Enrollment in another clinical with investigational drug or device - Inability to swallow pills - Adults unable to provide informed consent