Study Evaluating SARS-CoV-2 (COVID-19) Humoral Response After BNT162b2 Vaccine in Immunocompromised Adults Compared to Healthy Adults

The serious, even fatal, forms of COVID-19 preferentially affect elderly and fragile subjects. Among these populations at risk, people who are immunocompromised (either by a disease and / or its treatment) have a theoretical risk of responding less well to a preventive vaccination. The main objective of this study aims to compare the vaccine response of immunocompromised people with healthy subjects (non-immunocompromised), i.e. to assess the serum humoral response (titre and neutralizing capacity of the antibodies induced) following vaccination with ComirnatyTM (i.e. BNT162b2, an anti-SARS-CoV-2 vaccine from Pfizer BioNTech) in immunocompromised persons in comparison to healthy subjects (non-immunocompromised). Secondary objectives are as follows: * To evaluate the antibody response in the nasal mucosa (titre and neutralizing capacity of the antibodies induced, collected by means of a nasopharyngeal swab) following vaccination with ComirnatyTM in immunocompromised people as compared to healthy subjects (vaccinated either with two doses of ComirnatyTM or, in a subgroup, with one dose of Astra Zeneca's VaxzeriaTM followed by one dose of ComirnatyTM). * Evaluate the serum and mucosal antibody response (titre and neutralizing capacity of the antibodies induced) against emerging strains of SARS-CoV-2 (so-called Alpha, Beta, Gamma, Delta strains). * Evaluate the post-vaccination clinical protection against the risk of COVID-19 infection (incident cases after vaccination).