There are currently no proven vaccines or drugs for prevention of COVID-19. Chloroquine and hydroxychloroquine, drugs that have been used to treat malaria and a variety of rheumatological conditions have shown initial promise. Funded by the COVID-19 Bill & Melinda Gates Foundation, Wellcome and Mastercard Therapeutics Accelerator grant, the COPCOV study will enroll 40,000+ vital frontline health care workers and staff who have close contact with COVID-19 patients to determine whether chloroquine or hydroxychloroquine are effective in preventing COVID-19.