Allergen immunotherapy is a cornerstone in the treatment of allergic children. The clinical efficiency relies on a well‐defined immunologic mechanism promoting regulatory T cells and downplaying the immune response induced by allergens. Clinical indications have been well documented for respiratory allergy in the presence of rhinitis and/or allergic asthma, to pollens and dust mites. Patients who have had an anaphylactic reaction to hymenoptera venom are also good candidates for allergen immunotherapy. Administration of allergen is currently mostly either by subcutaneous injections or by sublingual administration. Both methods have been extensively studied and have pros and cons. Specifically in children, the choice of the method of administration according to the patient's profile is important. Although allergen immunotherapy is widely used, there is a need for improvement. More particularly, biomarkers for prediction of the success of the treatments are needed. The strength and efficiency of the immune response may also be boosted by the use of better adjuvants. Finally, novel formulations might be more efficient and might improve the patient's adherence to the treatment. This user's guide reviews current knowledge and aims to provide clinical guidance to healthcare professionals taking care of children undergoing allergen immunotherapy.

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE‐mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE‐mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well‐defined, highly pure molecules for component‐resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the “EAACI Molecular Allergology User's Guide” (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state‐of‐the‐art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Allergic diseases are common and frequently coexist. Allergen immunotherapy (AIT) is a disease‐modifying treatment for IgE‐mediated allergic disease with effects beyond cessation of AIT that may include important preventive effects. The European Academy of Allergy and Clinical Immunology (EAACI) has developed a clinical practice guideline to provide evidence‐based recommendations for AIT for the prevention of (i) development of allergic comorbidities in those with established allergic diseases, (ii) development of first allergic condition, and (iii) allergic sensitization. This guideline has been developed using the Appraisal of Guidelines for Research & Evaluation (AGREE II) framework, which involved a multidisciplinary expert working group, a systematic review of the underpinning evidence, and external peer‐review of draft recommendations. Our key recommendation is that a 3‐year course of subcutaneous or sublingual AIT can be recommended for children and adolescents with moderate‐to‐severe allergic rhinitis (AR) triggered by grass/birch pollen allergy to prevent asthma for up to 2 years post‐AIT in addition to its sustained effect on AR symptoms and medication. Some trial data even suggest a preventive effect on asthma symptoms and medication more than 2 years post‐AIT. We need more evidence concerning AIT for prevention in individuals with AR triggered by house dust mites or other allergens and for the prevention of allergic sensitization, the first allergic disease, or for the prevention of allergic comorbidities in those with other allergic conditions. Evidence for the preventive potential of AIT as disease‐modifying treatment exists but there is an urgent need for more high‐quality clinical trials.

The natural history of COVID‐19 caused by SARS‐CoV‐2 is extremely variable, ranging from asymptomatic or mild infection, mainly in children, to multi‐organ failure, eventually fatal, mainly in the eldest. We propose here the first model explaining how the outcome of first, crucial 10‐15 days after infection, depends on the balance between the cumulative dose of viral exposure and the efficacy of the local innate immune response (natural IgA and IgM antibodies, mannose‐binding lectin). If SARS‐CoV‐2 runs the blockade of this innate immunity and spreads from the upper airways to the alveoli in the early phases of the infections, it can replicate with no local resistance, causing pneumonia and releasing high amounts of antigens. The delayed and strong adaptive immune response (high‐affinity IgM and IgG antibodies) that follows, causes severe inflammation and triggers mediator cascades (complement, coagulation, and cytokine storm), leading to complications often requiring intensive therapy and being, in some patients, fatal. Low‐moderate physical activity can still be recommended. However, extreme physical activity and oral breathing with hyperventilation during the incubation days and early stages of COVID‐19 facilitates re‐inhalation and early direct penetration of high numbers of own virus particles in the lower airways and the alveoli, without impacting on the airway’s mucosae covered by neutralizing antibodies ("viral auto‐inhalation" phenomenon). This allows the virus to bypass the efficient immune barrier of the upper airway mucosa in already infected, young, and otherwise healthy athletes. In conclusion, whether the virus or the adaptive immune response reaches the lungs first is a crucial factor deciding the fate of the patient. This “quantitative and time‐/sequence‐dependent” model has several implications for prevention, diagnosis, and therapy of COVID‐19 at all ages.

Childhood asthma is frequently perceived as a disease with uniform clinical pathways. This perception might be an oversimplification. The aim of the present study was to investigate the incidence and natural course of wheeze over the first 13 yrs of life and analyse the risk factors predicting wheeze at 11–13 yrs of age.The Multicentre Allergy Study, a German birth cohort, recruited 1,314 children in 1990. Physical examinations, interviews on atopic diseases, immunoglobulin (Ig)E and lung function tests were performed up to 13 yrs of age.Complete data on the course of wheeze were available for 441 children. It was found that incidence of wheezing declined with age. The first wheezing episode was reported by 29, 9 and 9% of participants at ≤3 (early wheezers), 3–6 (late wheezers), and >6 yrs (very late wheezers) of age, respectively. Wheezing at the age of 13 yrs was associated with parental atopy, and with IgE sensitisation to common allergens, elevated total IgE and exposure to high levels of indoor allergens in early life. All these associations were remarkably stronger among early wheezers than among early nonwheezers.In conclusion, the relevance of an early expression of atopy as a predictor of wheezing at age 13 yrs declines with increasing age of wheezing onset.