Inclusion Criteria for patients:  Person aged 75 and over, Hospitalized in a long-term care unit participating in the study, Having agreed to be vaccinated with the BNT162b2 vaccine as part of the phase 1 vaccination campaign defined by the health authorities, Not having received any other vaccination or corticosteroid treatment during the 3 weeks preceding the start of the study, Having given their written consent to participate in the study, or having not expressed their opposition to participating and whose legal guardian has given their consent.  Inclusion Criteria for younger adults (priority care staff):  Staff who have agreed to be vaccinated with the BNT162b2 vaccine as part of the phase 1 vaccination campaign defined by the health authorities, Not having received any other vaccination or corticosteroid treatment during the 3 weeks preceding the start of the study, Having given their written consent to participate in the study.