This study aims to determine how long COVID-19 neutralizing antibodies can be detected in an elderly institutionalized population presenting fragility factors.

This study also aims to stratify seroconversion by immunological profiles of the elderly patients residing in the EHPAD. This stratification requires the measurement of immunological marker levels already described in immunosenescence and also involved in the development of certain chronic infectious diseases more common in the elderly population. This analysis will enable the investigators to describe an immunological, clinical and biological profile representing a patient who has developed an immunity against COVID 19. It will also help the investigators to understand the different mechanisms leading to a reduced immune response after a potential administration of a vaccine. Finally, it will help describe the immune profiles of elderly residents who presented with non-severe forms of COVID-19.

Inclusion Criteria:

• Residents of the EHPAD/USLD St Victor of the Amiens CHU who took part in the screening campaign (RT-PCR and serology) organized by the Amiens CHU
• residents who signed a consent form to participate in the study

Exclusion Criteria:

• The patient or his legal representative refused to participate in the study
• Heavily sedated patients