Difficulties in recruiting subjects were observed soon after the study was initiated. This difficulty was attributed to the decreased incidence of infections which occurred in the period following the first lock down.

This is a Italian, superiority, open label cluster-randomised, interventional clinical trial aimed at assessing whether the treatment with Hydroxychloroquine can reduce the percentage of symptomatic subjects compared to observation only in household members/contacts of COVID-19 patients (Group 1) and if the treatment with Hydroxychloroquine could be introduced in early phase COVID-19 population (Group 2).

The participants will be randomised to receive either:

Arm A) hydroxychloroquine vs Arm B) Observation (2:1 randomisation).

This is an open label, superiority, cluster-randomized Italian interventional clinical trial, evaluating the role of Hydroxychloroquine versus observation only in preventing infection to COVID-19 or treating early phase COVID-19 patients.

Each index case is randomised to either Arm A: Hydroxychloroquine or Arm B: observation in a 2:1 ratio on an open label basis. Participants in the same cluster receive the same intervention.

Study population is constituted by:

Group 1: Severe Acute Respiratory Syndrome (SARS) - Corona Virus (CoV)-2-exposed subjects , as household members/contacts of COVID-19 patients.

Group 2: Patients with COVID-19 asymptomatic or paucisymptomatic in home situation.

Inclusion Criteria:

1. Male or Female, aged >= 18 years

2. SARS-CoV-2-exposed subjects, as household members and/or contacts of COVID-19 patients (Group 1). In this group are included Health care professionals in contact with COVID-19 patients.

   or

3. COVID-19 patients, asymptomatic or paucisymptomatic in home situation who are not in treatment with any anti COVID-19 medication (Group 2)

4. Absence of any COVID-19 symptom in last week before randomization (fever >37.5°C, cough, dyspnea) (only for group 1 subjects)

5. Paracetamol treatment is accepted only for group 2.

6. Participant is willing and able to give informed consent for participation in the study (either recorded during a telephonic interview or signed in person) and agrees with the study and its conduct.

Exclusion Criteria:

1. Reported anamnesis for:

   1. Intolerance or previous toxicity for hydroxychloroquine/chloroquine
   2. Bradycardia or reduction rhythm of heart with arrythmias
   3. Ischemic heart disease
   4. Retinopathy
   5. Congestive heart failure under/with use of diuretics
   6. Favism or glucose-6-phosphate dehydrogenase (G6PD) deficiency
   7. Diabetes type 1
   8. Major comorbidities like advanced chronic kidney disease or dialysis therapy, known history of ventricular arrhythmias, any oncologic/hematologic malignancy.
   9. Severe neurological and mental illness

2. Any other contraindication to take hydroxychloroquine

3. Already taking chloroquine, hydroxychloroquine or analogous during the past 3 weeks

4. Use of other antiviral agents in the last 3 weeks

5. Subject with a positive test for SARS-CoV-2 (for Group 1)

6. Pregnant or lactating

7. Current use of medications with known significant drug-drug interactions: digoxin, hypoglycemic agents, anticonvulsant, Cyclosporine, Phenylbutazone, drugs that inhibit CYP2D6

8. Known prolonged QT syndrome or current use of drugs with known QT prolongation

9. Participation in another clinical trial with any investigational agents within 30 days prior to study screening.