Brief Summary:

The study is a double-blind, randomised, placebo-controlled trial that will be conducted in healthcare settings and other facilities directly involved in COVID-19 case management. We will recruit healthcare workers and other staff working in a facility where there are cases of either proven, or suspected, COVID-19, who can be followed reliably for 5 months. 40,000 participants will be recruited and we predict an average of 400-800 participants per site in 50-100 sites.

The participant will be randomised to receive either chloroquine or placebo (1:1 randomisation), or to hydroxychloroquine or placebo (1:1 randomisation). A loading dose of 10mg base/kg (four 155mg tablets for a 60kg subject), followed by 155 mg daily (250mg chloroquine phosphate salt/ 200mg hydroxychloroquine sulphate) will be taken for 3 months.

If the participant is diagnosed with COVID-19, they will take continue to take the study medication until:

90 days after enrolment (i.e., completion of kit)

hospitalised due to COVID-19 disease (i.e., not for quarantine purposes) in which case they will stop, or

disease (i.e., not for quarantine purposes) in which case they will stop, or advised to stop by their healthcare professional for other reasons

Episodes of symptomatic respiratory illness, including symptomatic COVID-19, and clinical outcomes will be recorded in the Case Record Form during the follow-up period.