Evaluation of the Immunogenicity and Safety of Ad26.COV2.S's COVID-19 Vaccine

The main objective of this phase II trial is to evaluate the humoral immune response induced by the Ad26.COV2.S vaccine in adults one month after complete vaccination regimen against SARS-CoV-2, compared younger (up to 45 years old) and elderly (55+ years old) populations.

200 participants will be included, 200 participants for each vacine. The age categories are 18 - 45 years, 55 - 64 years and 65+ years. The number of participants per age group will be distributed as follows 1:1:0,5. There will be no comparison between population on different vaccines.

Ad26.COV2 vaccine (200 participants) 18-45 years old, 80 participants 55-64 years old, 80 participants 65 years old or older, 40 participants

Participants in Ad26.COV2 arm receive intramuscularly as a single dose of 0.5mL.

Humoral vaccine immune responses, induced by Ad26.COV2.S vaccine, will be measured by ELISA at D0, M1, M2, M6, M12 and M24.

• Ad26.COV2.S (Biological), also known as Janssen, Johnson&Johnson: Recombinant vaccine, contains Adenovirus type 26 encoding the SARS-CoV-2 spike glycoprotein

Primary outcomes

• Anti-SARS-CoV-2 Spike immunoglobulin G (IgG) level [One month after complete vaccination schema]: Anti-SARS-CoV-2 Spike IgG level is measured using ELISA test

Secondary outcomes

• Anti-SARS-CoV-2 Spike IgG level [At inclusion (Day 0) and then 1, 2, 6, 12, and 24 months after inclusion]: Anti-SARS-CoV-2 Spike IgG level is measured using ELISA test
• Anti-SARS-CoV-2 immunoglobulin M (IgM) level [At inclusion (Day 0) and then 1, 2, 6, 12, and 24 months after inclusion]: Anti-SARS-CoV-2 IgM level is measured using ELISA test
• Neutralizing antibody level for SARS-CoV-2 [Inclusion (Day 0) and then 1, 2, 6, 12, and 24 months after inclusion]: Neutralizing antibody levels specific for SARS-CoV-2 and its variants (conventional in vitro neutralization and pseudo-neutralization assays)
• Fluorospot tests (type 1,2, and 17 helper T cell (TH1, TH2, TH17), Cytotoxicity) [Inclusion (Day 0) and then 2 and 6 months after inclusion]: Fluorospot tests (TH1, TH2, TH17, Cytotoxicity) Phenotyping of antigen-specific T cells by mass cytometry at Day 0 and Month 6 selected from the results of the Fluorospot test.
• Mucosal SARS-CoV-2 specific antibody levels [Inclusion (Day 0) and then 1, 2, 6, 12, and 24 months after inclusion]: Mucosal SARS-CoV-2 specific antibody levels by measuring IgA, IgM and IgG in saliva using specific ELISAs
• Determination of Epitope profile [Day 0 and Month 2]: Determination of epitope profile
• B cell response to vaccine [Day 0, Month 2, Month 6]: Determination of repertoire of B cells (stereotype clonotype)
• Measurement of ultrasensitive immunoglobulin A (IgA) and mucosal IgA and IgM functionality [Day 0 and then 1, 2, 6, 12, and 24 months after inclusion]: Measurement of ultrasensitive IgA in saliva by Photoring assay Measurement of mucosal IgA and IgM functionality by SARS-CoV-2 mucosal IgA- and IgM-specific antibody-dependent cell-mediated cytotoxicity (ADCC) test
• Rate of adverse events [Between month 1 and month 24 after inclusion]: Rate of adverse events of any grade attributable to the vaccine or vaccination occurring between Month 1 and Month 24
• SARS-CoV-2 infection [Date of inclusion until 24 months]: Occurrence of confirmed COVID-19 cases during participant follow-up

Other outcomes

• Measurement of specific B memory cells and T cell response [B memory cells: Day 0 and then 2,6, and 12 months after inclusion., T cell : Inclusion (D0) and then at 12 months after inclusion]: Measurement of specific B memory cells (Elispot B) and T cell response (Cytof analysis)
• Identification of predictive determinants of vaccine response [Day 0 until 24 months]: Identification of pre-existing immunity against other coronaviruses or respiratory pathogens, immunosenescence profile, transcriptomic, metabolomic and proteomic analysis, cytokine profile (IFNa), immune cell phenotype

Sex: All, ages: 18 Years to any, accepts healthy volunteers

Inclusion Criteria:

* Age between 18 and 45 years old or 55 years and older
* Be eligible to receive one of the study vaccines as part of the trial
* Understand and agree to comply with study procedures (visits, telephone calls)
* Agree not to participate in any other vaccine study during the time of the study
* Give written informed consent prior to any examination performed as part of the trial

Exclusion Criteria:

* Positive SARS-CoV-2 antigenic test
* Positive SARS-CoV-2 polymerase chain reaction (PCR) results less than 48 hours old
* History of infection by SARS-CoV-2 confirmed by antigenic test or PCR within 3 months prior to inclusion
* Symptoms compatible with infection to SARS-CoV-2: sick or febrile participants (body temperature ≥ 38.0°C)
* Pregnant or breastfeeding woman
* Known chronic disease impacting the participant's immune response (uncured cancer, human immunodeficiency virus (HIV), hepatitis B virus (HBV) or hepatitis C virus (HCV) infection)
* Anti-coagulant treatment
* Immunosuppressive treatment
* Contraindication to the proposed vaccine (according to RCP)
* Previously received at least one injection of a SARS-CoV-2 vaccine
* Patient having received immunoglobulin or another blood product within 3 months prior to inclusion
* A history of serious adverse vaccine reactions (anaphylaxis and associated symptoms such as rash, breathing difficulties, laryngeal edema, or a history of allergic reaction that may be exacerbated by a component of the SARS-CoV-2 vaccine)
* Any condition that, in the opinion of the investigator, may adversely affect the well-being of the participant and interfere with the purpose of the study

• Odile Launay, Study chair, Innovative clinical research network in vaccinology (I-REIVAC)
• Samba Sow, Principal investigator, Center for Vaccine Development-Mali (CVD-Mali)