The purpose of the study is to evaluate the immunological response and tolerance of 3 vaccine strategies against meningococcus B, a potentially fatal invasive infection.

Currently, in France, no immunogenicity data on Meningococcal B vaccines, neither with Bexsero® nor with Trumenba®, are available in asplenic patients, population at high risk of infection.

As asplenic individuals (all causes) show less optimal immune response to conjugate meningococcal C vaccine compared to matched controls. [4], we hypothesize that a similar less optimal response may be expected for MenB vaccines among asplenic subjects. .

That is why, we proposed in this study to evaluate two reinforced strategies with 3 administrations (M0, M1, and M6) of Bexsero® or Trumenba ®. Moreover, the study will also allow exploring the persistence of the immune response in this population. Indeed, few data are available on this persistence in the general population.

Inclusion Criteria:

1. Male or female, >=18 to <=75 years old.
2. Asplenic patient (for at least 2 weeks) with Howell Jolly bodies visible on blood film
3. Splenectomy confirmed by consultation and/or hospitalization report or the ultrasound if it has been performed during the routine follow-up
4. Women of childbearing age must have an effective contraception during the first 9 months of the study.
5. Participants must give written consent prior to any trial procedure
6. Participants must be covered by social security regimen or equivalent.
7. Participants will be followed during the 4 years from the inclusion visit.

Exclusion Criteria:

1. History of meningococcal vaccination B.
2. History of anaphylaxis post vaccination.
3. Known allergy to any components (active substances or excipients) of both vaccines.
4. Patients who cannot stop antibiotics 3 days before blood collection.
5. Participants who have received any another vaccines within 4 weeks prior to immunization or who are planning to receive any vaccine within the first 7 months of the study (except the meningococcal ACWY vaccine, the anti-pneumococcal vaccine, the Haemophilus influenzae type B vaccine, the anti-Covid-19 vaccine), annual influenza vaccination which is permitted 2 weeks before and after each vaccination visit of the study and then allowed at any time during the study follow up).
6. Parenteral Ig within the 3 months prior to VS or planned during the study.
7. Chemotherapy agents within 6 months prior M0 or planning to take any during the study.
8. Steroids (> 10mg/day; > 14 days) within the month preceding M0 or planning to take any during the study.
9. Any pathology or condition that may impair the immune response, apart from splenectomy: immunosuppressive therapy in progress or in the 6 months prior to inclusion, hematopoietic stem cells allo / autograft, primary immunodeficiency, nephrotic syndrome, evolutive cancer, cirrhosis, known infection to HIV;
10. Thrombocytopenia or any coagulation disorder contra-indicating intramuscularly injections.
11. Pregnancy, breastfeeding or positive pregnancy test up to 7 months after inclusion.
12. Severe acute febrile illness within the week before inclusion.
13. Registration for any other clinical trial throughout the trial period except observational study.

The trial will be open label. However, the assessment of the primary and secondary immunological endpoints will be carried out blind from the treatment arm.