Inclusion Criteria:  Age ≥ 18 years Having received a first dose of one of the two mRNA vaccines (Pfizer-BioNTech or Moderna) as recommended. For whom a 2nd dose of mRNA vaccine is planned within 4 to 6 weeks (according to the recommendations of the HAS and the ANSM). Without a history of SARS-CoV-2 infection (negative PCR, negative antigen test or negative chest CT or SARS-CoV-2 serology) Healthy or in stable health if pre-existing medical history. Stable health is defined as an existing disease that has not required a significant change in treatment or hospitalisation for worsening in the 3 months prior to inclusion, and for which neither a significant change in treatment or hospitalisation for worsening of the disease is envisaged in the near future Able to understand and comply with the research procedures as judged by the investigator Informed consent signed by the participant and the investigator. Person affiliated to a social security scheme.  Exclusion Criteria:  History of SARS-CoV-2 infection at the inclusion visit or between the 2 vaccine doses (documented by positive PCR, positive antigen test or positive chest CT or positive SARS-CoV-2 serology. Acute febrile infection (body temperature ≥ 38.0°C) within the previous 72 hours and/or with symptoms suggestive of COVID-19 or case contact within the last 14 days prior to the inclusion visit. Sick or febrile subjects may be re-invited for a new inclusion visit during the inclusion period when they no longer have these symptoms) Immunosuppressive medications such as corticosteroids at a dosage > 10 mg prednisone equivalent/day (excluding topical preparations and inhalers) within 3 months prior to inclusion or within 6 months for chemotherapy. Treatment with immunoglobulin or other blood product within 3 months prior to inclusion or with planned administration of immunoglobulin or blood product before the end of the study. Known HIV, HCV or HBV infection. Any immunosuppressive condition, such as cancer, that may reduce the immune response. The use of experimental Ig, experimental monoclonal antibodies or convalescent serum is not permitted during the study. Pregnant or breastfeeding. Participation in any other research involving humans (Jardé 1 or Jardé 2) within 4 weeks prior to the inclusion visit Person subject to a legal protection measure (guardianship, curatorship or safeguard measure). History of severe adverse reactions after vaccine administration including anaphylactic reaction and associated symptoms such as rash, difficulty breathing, angiodema and abdominal pain, or a history of allergic reaction that may be exacerbated by a component of the SARS-COV-2 vaccine at the time of the first vaccine injection Participant who has been vaccinated against BCG in the previous year. Having received a vaccination within 4 weeks prior to the first injection or scheduled to receive a licensed vaccine 4 weeks after the last injection. History of severe allergic manifestations Any bleeding disorder considered to be a contraindication to intramuscular injection or having had a phlebotomy