The purpose of this study is to determine whether hydroxychloroquine is an effective prophylactic regimen to prevent SARS-CoV-2 infection among healthcare workers. Participants will be randomized into two parallel groups. The first arm will evaluate the use of hydroxychloroquine every-other-day plus standard measures of protection for the prevention of SARS-CoV-2. The second arm will evaluate the use of standard measures of protection for the prevention of SARS-CoV-2. The target enrollment is 320 participants. Each study participant will be monitored for SARS-CoV-2 seroconversion in weekly visits or for the development of COVID-19 symptoms for 8 weeks.

Inclusion Criteria:

1. Healthcare workers in service during the COVID-19 outbreak including medical, nurse, technical, and auxiliary staff.
2. Negative rapid serologic and molecular testing for SARS-CoV-2.
3. Written informed consent.

Exclusion Criteria:

1. Presents COVID-19 symptoms including cough, fever, myalgias, headaches, loss of smell, and taste.
2. Prior (last 30 days), current or planned use (during study period) of hydroxychloroquine, chloroquine sulfate, or azithromycin.
3. Known cardiac disease or a history of prolonged QT syndrome.
4. Known allergy or intolerance to hydroxychloroquine and/or chloroquine sulfate.
5. Use of concomitant medications that are contraindicated with the use of hydroxychloroquine.
6. Other reported medical conditions, such as glucose-6-phosphate dehydrogenase deficiency, hepatic or renal insufficiency, or visual acuity or field disturbances, that make study participation not in the individual's best interest.