The investigators performed in April 2020, a screening campaign of asymptomatic staff working in elderly nursing homes in Paris, France, where the virus had been circulating actively in March and April 2020. Among 241 employees tested in four nursing homes, 32 (13.2%) were asymptomatic carriers of SARS-Cov-2.~Few data are available concerning the humoral immune response of asymptomatic carriers, the elicitation and duration of neutralizing antibodies and the duration of protection.~The main objective of this study is to describe the SARS-Cov-2 asymptomatic employees with positive immunoglobulin G (igG) serology at month 1-2 post infection.~Secondary objectives are~To describe the proportion of asymptomatic persons with SARS-Cov-2 antibodies month 3 and 6 post infection~To compare the proportion of persons with SARS-Cov-2 antibodies between asymptomatic and asymptomatic carriers at M1-2 post infection, M3 and M6 post infection~To determine the factors associated with the appearance of antibodies ( viral load, age, sex, previous history, habitus..)~To study the neutralizing capacities and immune-profiling of SARS-Cov-2 antibodies in vitro~To evaluate the occurrence of Coronavirus Disease 2019 (COVID-19) reinfections in asymptomatic carriers during the second wave.~The design will be a case control study between~Cases: SARS-Cov-2 asymptomatic nursing homes employees~Controls: cohort of patients with a symptomatic COVID-19, preferably recruited in nursing homes or in case of difficulties in the virology service of COCHIN Hospital.
The investigators performed in April 2020, a screening campaign of asymptomatic staff working in elderly nursing homes in Paris France (EHPAD), where the virus had been circulating actively in March and April 2020. Among 241 employees tested in four nursing homes, 32 (13.2%) were asymptomatic carriers of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-Cov-2).~Few data are available concerning the humoral immune response of asymptomatic carriers, the elicitation and duration of neutralizing antibodies and the duration of protection.~The purpose of the study is to determine whether these asymptomatic persons develop a humoral immune response, whether this immune response is durable and whether it is protective against the risk of reinfection