Our study aims to identify an optimal vaccination strategy for immunocompromised CIBD patients by combining use of a conjugate vaccine, Prevenar13® and a polysaccharide vaccine, PSV-23®. We will compare the use of one or two doses (M0 +/- M2) of Prevenar13® combined with a later PSV-23® injection (M4) on vaccination immunogenicity measured by antibody titer against at least nine of the thirteen pneumococcal serotypes contained in Prevenar13®. We also want to evaluate the immunological impact of these different strategies in their capacity to stimulate a memory B anti-pneumococcal response more effectively. With this aim, we are studying all immunological functional aspects of the antibodies and B lymphocytes induced by the two vaccine strategies.