Comparison of different hydroxychloroquine dosages vs. placebo in three cohorts (outpatients, inpatients, healthcare workers a risk). Double-blind RCT for outpatients and healthcare workers and open-label RCT for inpatients (NCT04329923, not yet recruiting). Primary endpoints: (a) release from quarantine (outpatients, follow-up 14 days); (b) discharge (inpatients, follow-up 14 days); (c) development of COVID-19 (healthcare workers, follow-up 2 months).