ROLL'YN-OMA: an Observational Study in Patients Treated by Omlyclo®, an Omalizumab Biosimilar

Inclusion Criteria: * Be an adult (aged 18 years or older at the time of inclusion) receiving specialist care and diagnosed with one of the following conditions: Severe asthma, Chronic Spontaneous Urticaria * Have been treated for at least 6 months prior to inclusion with the reference omalizumab for the relevant condition (Severe asthma or Chronic Spontaneous Urticaria). * Have been stable for at least 3 months according to the prescribing physician, with the disease controlled or in clinical remission based on the disease-specific activity score: Severe asthma: ≤ 1 course of oral corticosteroids per year related to disease worsening, without hospitalization, and ACQ \< 1.5 and FEV1 ≥ 80% of the patient's most recent values/ Chronic Spontaneous Urticaria : UCT ≥ 12 * For whom the specialist physician has decided to switch to OMLYCLO® (biosimilar developed and marketed by Celltrion) on the day of patient inclusion (shared medical decision independent of the study). * Be able to start treatment within a maximum of 60 days following inclusion. * Have an email address. * Have a mobile phone number. * Be able to understand and complete questionnaires in French. * Not object to participating in the study. * Be affiliated with a French Social Security scheme or be a beneficiary of such a scheme Exclusion Criteria: * Patients under guardianship or trusteeship, or otherwise deprived of liberty. * Pregnant women or women of childbearing potential with a desire to become pregnant during treatment with OMLYCLO®. * Patients who, at the time of inclusion, are participating in a clinical trial or another clinical study that prohibits simultaneous participation in other studies. * Contraindication to the study products.