Inclusion Criteria:  Age ≥ 18 years Adult in a healthy condition or with a stable health status if pre-existing medical history. Stable health status is defined as an existing disease that has not required a significant change in treatment of hospitalization for worsening in the 3 months before enrollment, and for which neither a significant change in treatment or hospitalization for worsening is expected in the near future For women of childbearing age: a negative highly sensitive pregnancy urinary test during the inclusion visit AND use of an effective contraceptive method prior to vaccination and until at least 12 weeks after the vaccination Who has received 2 doses of mRNA vaccine (Pfizer-BioNTech) with an interval of 3 to 6 weeks Second dose of mRNA vaccine (Pfizer-BioNTech) administered 6 months +/- 1 month before the booster dose Understands and agrees to comply with the study procedures Written informed consent signed by both the participant and the investigator Subject affiliated to the French Social Security System.  Exclusion Criteria:  Acute febrile infection (body temperature ≥ 38.0°C) within the previous 72 hours and/or presenting symptoms suggestive of COVID-19 within the previous 28 days, or having been in contact with an infected individual for the last 14 days before the inclusion visit; Virologically documented history of COVID-19 (PCR or serology); Immunosuppressive therapy such as corticosteroids > 10 mg prednisone equivalent/day (excluding topical preparations and inhalers) within 3 months prior to inclusion or within 6 months for chemotherapies; Treatment with immunoglobulins or other blood derivatives within 3 months prior to inclusion or scheduled administration of immunoglobulins or blood derivatives before the end of the study; Known HIV, HCV or HBV infection; Any medical condition, such as cancer, that might impair the immune response; Use of experimental immunoglobulins, experimental monoclonal antibodies or convalescent plasma is not permitted during the study; Pregnancy or breastfeeding currently ongoing; History of severe adverse events following vaccine administration including anaphylactic reaction and associated symptoms such as rash, breathing problems, angioedema, and abdominal pain, or a history of allergic reaction that could be triggered by a component of the SARS-COV-2 vaccine at the time of the first vaccine injection; Participant who has received BCG (tuberculosis) vaccine within the previous year; Has received a vaccine within 4 weeks prior to the boost injection or is scheduled to receive a registered vaccine 4 weeks after the boost injection Any bleeding disorder considered as a contraindication to an intramuscular injection, previous phlebotomy, or receipt of anticoagulants Participation in other research involving humans (French classification Jarde 1 or Jarde 2) within 4 weeks prior to the inclusion visit, or participation in any other vaccine trial Subject under legal protection (e.g. guardianship, tutorship)