Vaccination against COVID-19 is a major public health issue to control the epidemic and reduce the number of severe infections and deaths. Three vaccines currently received use authorization in France: two mRNA vaccines and one recombinant viral vector vaccine. Immunogenicity data demonstrate that they induce the development of neutralizing antibodies and IgG directed against the viral S1 protein and the receptor binding domain (RBD). However, there are currently no data on the persistence over time of the humoral response induced by vaccination, and data are still incomplete on cellular immunogenicity. No immune correlate of protection has been established for COVID-19.

In addition, these data come from assays carried out with current vaccines developed against a lineage of SARS-CoV-2 known as wild type (without genetic mutations).

The main objective of this study is to monitor in hospital staff the temporal evolution of humoral immunity induced by anti-COVID-19 vaccines by using enzyme-linked immunosorbent assays (ELISA), at 3, 6, 12 and 24 months after the last injection of vaccine.

• All medical, para-medical, medico-technical and administrative staff of the Clermont-Ferrand university hospital will be informed of the protocol through intra-hospital communication. The inclusion visit will be scheduled within 3 months +/- 14 days after the last injection of the vaccine. For volunteers who have not received their first injection, they will be offered to participate in the sub-study including an additional visit on the day of vaccination. They will be free to accept or refuse.

• As recruitment is consecutive, an anonymous list of potentially eligible subjects (with demographic data: age, sex; nature of the vaccine received) will be kept, in order to verify afterwards if the sample is representative.

• The study includes:

  1. Five visits over 21 months, 6 over 24 months for the subgroup included on the day of vaccination

  2. An interview with an investigator during the first visit, to collect the following data: hospital function, age, sex, weight, height, possible comorbidities exposing to a serious COVID-19 infection, possible COVID-19 infection prior to vaccination, date of vaccination and type of vaccine

  3. A self-questionnaire to update clinical data if necessary during the following visits

  4. A blood test at each visit, i.e. 2 tubes of 5 mL (antibody assays) and 4 tubes of 1 mL (cellular immunity assay).

     Blood samples will be stored at -80°C, before destruction at the end of the study.

• In the case of suspecting symptoms of COVID-19 during follow-up, molecular testing of SARS-CoV-2 infection will be offered and performed from nasopharyngeal swab or saliva sample.

Inclusion Criteria:

• Adult person, man or woman, staff of the Clermont-Ferrand University Hospital (medical or paramedical, medico-technical or administrative caregiver), having received the second dose of vaccine (or the single dose if the single-dose vaccination schedule) against COVID- 19 3 months +/- 15 days before the inclusion visit, as part of the national vaccination campaign, regardless of the type of vaccine administered.
• For the subgroup included before vaccination (study of the pre-vaccination cellular response): Adult person, man or woman, staff of Clermont-Ferrand University Hospital (medical or paramedical, medico-technical or administrative caregiver), receiving the 1st injection on the same day or in the 7 days before the inclusion visit, regardless of the type of vaccine administered
• Commitment to respect the schedule of visits provided for in the research protocol
• Able to give informed consent to participate in research
• Affiliation to a social security scheme

Exclusion Criteria:

• Pregnancy or breastfeeding in progress at inclusion, or planned during follow-up
• Person under guardianship, guardianship or legal protection
• Whether the vaccine received was experimental or not authorized
• Refusal of participation