Strategy B: administration of vedolizumab 300mg by infusion at baseline, 14 days, 42 days and 60 days, followed by a dose of 108mg every fortnight by subcutaneous injection.

Biomarkers are considered to be standardised if the following are observed

- normalisation of faecal calprotectin: faecal calprotectin < 250 µg/g at week 24.

Biomarkers are considered to be standardised if the following are observed

- Normalisation of serum C-reactive protein (CRP) : serum CRP < 5 mg/L at week 24 ;

A patient is considered to be in endoscopic remission if they have:

- a CDEIS score < 3 at week 24 using ileocolonoscopy ; The CDEIS is an index of the severity of intestinal lesions caused by Crohn's disease.

The CDEIS ranges from 0 to 44 0: no lesions 44: most severe lesions Endoscopic remission defined by a CDEIS ≤ 7

A patient is considered to be in endoscopic remission if they have:

- a Lewis score < 135 at week 24 in the small bowel using VCE (video endoscopy); The Lewis score analyses 5 mucosal parameters for each of the four segments of the small bowel (duodenum, jejunum, proximal and distal ileum): erythema, oedema, presence of nodular lesions, ulcerations and stenosis. A Lewis score < 135 indicates inactive disease.

A patient is considered to be in endoscopic remission if they have:

- no ulceration using endoscopic video capsule (VCE) at week 24;

A patient is considered to be in endoscopic remission if they have:

- no activity on MRI at week 24 (defined as segmental MaRIA score < 7); The MaRIA (Magnetic Resonance Index of Activity) scoring system is used to assess ileocolic Crohn's disease activity on contrast-enhanced MRI enterography. The segmental index represents the severity of disease in a segment of the bowel, while assessing six defined anatomical regions that can be combined to form an overall MaRIA index.

The cut-off points for the MaRIA score are as follows:

moderate disease: ≥7 severe disease: ≥11

A patient is considered to be in endoscopic remission if they have:

- no bowel thickness on ultrasound at week 24 (< 3mm with no other signs of activity).

Compare treatment failure at week 24 or week 52 in the 2 groups.

Treatment failure is defined as:

• The performance of a CD-related surgery between inclusion and week 24 ;
• OR use of steroids between baseline and week 24;
• OR treatment dose optimisation between inclusion and week 24;
• OR a change in treatment between inclusion and week 24.

Compare the percentage of adverse events in both arms at week 52

Symptomatic remission at week 24 is a composite criterion measured by PRO2 defined as: Stool frequency (SF) < 3 with abdominal pain score (AP) < 2 at week 24; AND absence of therapeutic failure between inclusion and week 24.

Compare evolution of IBDQ-32 in the two groups of patients between inclusion and week 24.

The IBDQ-32 questionnaire consists of 32 questions. Each question is answered on a scale from 1 to 7, with 1 being the lowest score and 7 the highest. Adding up the different scores gives a total score, ranging from 32 (worst score) to 224 (best score). The higher the score, the better the quality of life.

Compare rates of clinical and biomarker remission at week 12 and week 52.

Rate of Mucosal remission at week 24. Mucosal remission is definied by ;

• a CDEIS score < 3 at week 24 using ileocolonoscopy ; The CDEIS is an index of the severity of intestinal lesions caused by Crohn's disease.
• Or a Lewis score < 135 at week 24 in the small bowel using VCE (video endoscopy)
• Or no ulceration using endoscopic video capsule (VCE) at week 24;
• Or no activity on MRI at week 24 (defined as segmental MaRIA score < 7);
• Or no bowel thickness on ultrasound at week 24 (< 3mm with no other signs of activity).

Analyze the CDST score for prediction of remission under vedolizumab and adalimumab optimization.

A CDST score :

• < 13 points is considered a low probability of remission;
• Between 13 and 19 points is considered an intermediate probability of remission;
• > 19 points is considered a high probability of remission.

Compare the efficacy of each strategy based on baseline serum ADA levels, classified into three groups: Pharmacodynamic failure: Therapeutic level of ADA in blood (> 7.5 µg/mL) Pharmacokinetic failure: Subtherapeutic level of ADA in blood (< 7.5 µg/mL) Immunogenic failure (undetectable serum ADA level with the presence of anti-ADA antibodies >50 ng/mL).