Study aim: The comparisson of the prevalence and the severity of COVID-19 in staff with encounter to the COVID patients in the case and control groups Design: Two arm parallel-group phase-2 clinical trial with outcome assessment in 320 volunteer staff who encounter with COVID-19 patients divided into case group( use 400 mg/week hydroxychloroquine as prophylaxis) and control group (without any drug) Settings and conduct: In this study, the staff of Seyedoshohada, Isabnemaryam, Khorshid, and Amin hospitals in Isfahan city who are an encounter with COVID-19 patients divided into the case (weekly use of Hydroxychrolokin for 3 months) or control( without any drugs) groups and follow-up during 6 months. The prevalence of affection or the severity of illness will be compared in the two groups. Participants/Inclusion and exclusion criteria: Exclusion Criteria 1- Treatment with other antiviral drugs at the same time, except for the drugs prescribed in the national protocol 2 - Concomitant diseases: malignancy, advanced heart failure, cirrhosis, people under dialysis, stroke, Alzheimer's, progressive chronic neurological diseases 3- Evidence of multiorgan failure 4- Pregnancy or lactation Intervention groups: Case group: the volunteer staff encounter with COVID-19 patients who use the hydroxychloroquine as prophylaxis in the dose of 400 milligrams per week for 3 months Control group: The staff who encounter with COVID-19 patients without any prophylaxis treatment Main outcome variables: prevalence of COVID-19 onset; the severity of COVID-19