Real-world evidence of allergen immunotherapy.

Purpose of review: The full understanding of the long-term effectiveness and safety of allergen immunotherapy (AIT) for allergic respiratory diseases cannot be achieved through randomized controlled trials (RCTs) alone. However, real-world studies designed as registries can complement RCTs.

Recent findings: The significance of registries is highlighted by their potential to reassess contraindications and collect data on adult and pediatric patients with multiple comorbidities who are often excluded from RCTs.

Summary: AIT is the sole disease-modifying therapeutic approach capable of inducing tolerance and offering a long-term response to allergens. AIT has been shown to play a role in arresting the 'allergic march' in young people, which reduces the risk of developing asthmatic clinical manifestations. Although RCTs are considered the gold standard for evaluating the efficacy and safety of AIT, their duration is usually too short (seldom lasting more than 1 year) to assess the long-term effects of AIT. Several long-term studies show that AIT's effect depends strongly on its use duration.