Low enrollment.

The primary objective is to determine the clinical efficacy of Chloroquine (CQ) in health care workers with moderate to high risk of exposure to COVID-19 in preventing symptomatic COVID-19 infections. Secondary endpoints will explore the efficacy of CQ in preventing any infection as defined by seroconversion to positive anti-COVID antibody status.

Chloroquine (CQ) phosphate is an immunomodulatory drug that has been approved by the FDA for prophylaxis of and treatment of malaria, treatment of lupus erythematosus, and treatment of rheumatoid arthritis. Anecdotal data and in-vitro studies suggests potential benefit of chloroquine in treating COVID-19 patients. The use of CQ to treat COVID-19 patients have been demonstrated to be effective in inhibiting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The use of CQ in health care workers with moderate to high risk of exposure to COVID-19 in could prevent symptomatic COVID 19 infections. 350 participants will be randomized (like a flip of a coin) to a 3 month chloroquine versus an identical course of placebo. A placebo is a sugar pill which has no active ingredient. will attend one in person visit during month 0 for screening and randomization, and if possible during the last visit at month 3. During month 1 and 2 the in person visits are optional and the PI can follow up with subjects through telemedicine or phone call. Informed consent, inclusion/exclusion criteria, demographic, medical/ disease history/ comorbidity/ medical records review, prior/ concomitant meds and procedures, and adverse events will be collected from patient during screening visit 1 (month 0). Limited physical assessment, vitals, blood serum, investigational product compliance review, assessment of adverse events, serious adverse events, adverse events of special interest, and endpoint assessments are also collected during visit 1. Prior/concomitant medications and procedures, adverse events, study drug compliance review, adverse events of special interest, adverse events of special interest and endpoint assessments will be reviewed at every visit. Blood serum will be collected during visits 1 (month 0) and at visit 4 (month 3) if subject can come to the visit physically. By the end of the study, the investigators hope that there is decrease of symptomatic illness in at risk healthcare workers and a decrease in symptomatic COVID infection.

Inclusion Criteria:

1. Age ≥18 years,
2. Employment by New York Presbyterian Hospital
3. Clear assignment to areas of the hospital that involve patient contact and possible exposures for at least 2 days a week >/= 8 hours a day

Exclusion Criteria:

1. Individuals who are taking CQ for other indications
2. New use of NSAIDs
3. High risk background medications not limited to immunosuppressive regimens, steroids, anti-B cell therapies, anti-cytokine therapies, chemotherapies, Janus Kinase (JAK)-inhibitors
4. Individuals with a history of retinopathy that would contraindicate the use of CQ
5. Known allergy to CQ or chloroquine
6. Known QT prolongation and torsades de point
7. Individuals who are pregnant or nursing

The study was terminated before participants could be assigned to any Arm.

Up to 3 months

The study was terminated before participants could be assigned to any Arm, therefore Adverse Events cannot be reported per Arm.

Study was stopped early due to poor enrollment. Data was not collected and therefore not analyzed.