Common inclusion criteria:  Age ≥ 18. Health care employees working in the EHPAD who consulted in the Hotel Dieu Hospital Affiliated with a health insurance Informed information and consent  Inclusion Criteria for Cases (asymptomatic COVID-19 patients) :  Health care workers screened SARS-Cov-2 positive for NASopharyngeal swaths during screening campaigns for EHPAD staff. Having carried out a follow-up serology (M1 and M2) within the Hotel Dieu. Having never developed symptoms of COVID-19 or have developed some symptoms undetected before screening: fever, transient fatigue, rhinorrhea, symptoms that may be mistaken for a common winter cold (no respiratory symptoms or prolonged fever)  Inclusion criteria for controls (symptomatic COVID-19 patients) :  Health care workers tested positive for polymerase chain reaction assay (PCR) SARS-Cov-2 during screening campaigns for EHPAD staff at the Hotel Dieu. Having carried out a follow-up serology (M1 and M2) within the Hotel Dieu.  COVID-19 symptoms defined by:  At least two major signs of COVID-19 among: > fever, cough, chest tightness, bilateral pneumonia, anosmia, loss of taste. or a major sign and three minor signs among: headache, severe fatigue, diarrhea, odynophagia, rhinorrhea, suggestive skin signs.  It is part of the database of the virology department of Cochin Hospital (in case of failure to recruit health care workers in the EHPADs).  *Exclusion criteria :  Refuse to participate or inability to obtain informed consent. under guardianship, curators negative SARS-COV-2 PCR Pregnancy