PGATE for patients ≥ 12 years of age: an internally developed and validated instrument allowing patients to rate their opinion and perceived treatment effect. Ratings are on a 5-point Likert scale from 1 being "Poor" and 5 being "Excellent".

EASI is a validated measure used to assess severity and extent of AD at each body region by multiplying the lesions characteristics score x the body area score x multiplier. Four AD disease characteristics -erythema, thickness (induration, population, and oedema), scratching (excoriation), and lichenification - will each be assessed for severity by the observing physician, as follows: 0 = none, absent; 1=mild (just perceptible); 2=Moderate (obvious); 3=Severe. The area score ranges from 0 to 6 is determined as follows: 0= 0% (no active eczema in region); 1= 1-9%; 2= 10-29%; 3= 30-49%; 4= 50-69%; 5= 70-89%; 6= 90-100% (entire region affected by eczema). The multiplier is determined according to the region affected and the age of the patient: 0.1 or 0.2 for patients < 8 years old (head/neck), 0.2 (upper limbs), 0.3 (trunk), 0.4 or 0.3 for patients < 8 years old (lower limbs). A higher score means higher AD severity. Scores range from 0 (no disease) to 72 (maximal disease severity).

ADCT for patients aged ≥ 12 years of age: a validated, brief and easily scored tool consisting of six concise questions allowing to rate the different dimensions of patient-perceived AD control, to foster communication between patients and their physicians and help appropriate decision-making. The instrument includes 6 items, with a 7-day recall period: overall severity of symptoms, frequency of intense episodes of itching, severity of bother, frequency of sleep impact, severity of daily activities impact and severity of mood or emotions impact. Each item is rated on a 5-point Likert scale, ranging from 0 (none/ not at all/ no nights) to 4 (very severe/ everyday/ extremely/ every night); the total score ranges from 0 to 24, which is the summation of the responses to all the items. A total score of ≥7 points was derived as the threshold to identify patients "not in control", based on optimal sensitivity/ specificity values. The higher the score, the less AD is controlled.

Itch assessment (Worst-Itch Numeric Rating Scale, WI-NRS) will be rated from 0 to 10 on average during the past 7 days (adult, pediatric and adolescent patients), completed by the observing physician after questioning of patient; 0 = no itch and 10 = the worst imaginable itch.

NRS sleep disturbance will be rated from 0 to 10 on average during the past 7 days (adult, pediatric and adolescent patients), completed by the observing physician after questioning of patient; 0 = "sleep not disturbed at all" (best possible sleep) and 10 = "sleep extremely disturbed (worst possible sleep)".

PGADS for patients ≥ 12 years of age: an internally developed and validated instrument allowing to the patients to rate their AD-related overall well-being. Patients will be asked: "Considering all the ways in which your eczema affects you, how well are you doing?" Response choices will be from 1 being "Poor" to 5 being "Excellent".

CGAD for patients 6 to 11 years of age: an internally developed and validated instrument allowing to the caregivers to rate their child's AD-related overall well-being. Caregivers will be asked: "Considering all the way in which the eczema affects your child, how well is your child doing?". Response choices will be 1 being "Poor" to 5 being "Excellent".

DLQI for patients ≥ 16 years (or cDLQI for patients < 16 at baseline) are 10-item, validated questionnaire used in clinical practice and clinical trials to assess the impact of AD disease symptoms and treatment on quality of life in adults and pediatrics, respectively. The format is a simple response (0 to 3 where 0 is "not at all" and 3 is "very much") to 10 items, which assess quality of life over the past week, with an overall scoring system of 0 to 30; a high score is indicative of a poor quality of life. Patients 6-11 years old will be assisted for questionnaire completion. A cDLQI's cartoon version could be also used for patients from 6 to 11 years old. If a patient turns 16 years old during the study, they will switch to DLQI.

DFI is a 10-item, validated questionnaire assessing the impact of AD on the QoL of the parents/legal representatives and family members of affected children. The format is a simple response (0 to 3 where 0 is "not at all" and 3 is "very much") to 10 items, which assess Quality of Life (QoL) over the past week, with an overall scoring system of 0 to 30; a high score is indicative of a poor QoL. It is designed to be completed by adults (aged 16 years or over) who have a child (up to and including the age of 15 years 11 months) in the family with atopic dermatitis.

The EQ-5D-3L is completed by patients≥18 years old and by parent/legal representative of patients<18 years old. It consists of 2 parts:

• The EQ-5D descriptive system has five dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each has 3 levels: no problems, some problems, and extreme problems. The patient selects the most appropriate statement in each of the five dimensions, resulting in a 1-digit number for each dimension. The digits for the five dimensions can be combined into a 5-digit number that describes the patient's health state.
• The EQ VAS records the patient's self-rated health on a vertical visual analogue scale where the endpoints are labelled 'Best imaginable health state' and 'Worst imaginable health state'. The VAS can be used as a quantitative measure of health outcome that reflects the patient's own judgement. The scale is numbered 0 to 100. A higher value represents better health and a lower value represents worse health.

WPAI-AD for adults and WPAI-CIQ-AD for adolescents is a questionnaire designed to assess the impact of AD on the patient's productivity. The WPAI-AD is the version of the original generic WPAI that is specific to AD. It is a 6-item, validated questionnaire to measure impairments in work and activities over a 7-day recall period. The WPAI-AD outcomes are expressed as impairment percentages, with higher numbers indicating greater impairment and less productivity. If a patient turns 18 years old during the study, this one will switch to WPAI-AD.

AEs for dupilumab and/or concomitant treatments will be collected throughout the study.

Drug survival is defined as the time from the start of treatment to the end or discontinuation of treatment with no changes. If a patient has multiple drug survival events for the same treatment, the longest drug survival will be used in the data summarization. The drug survival will be illustrated using a Kaplan-Meier plot.