Efficacy of sublingual swallow immunotherapy in children with severe grass pollen allergic symptoms: a double-blind placebo-controlled study

Background: Local application of allergen extracts in specific immunotherapy is accompanied by increased compliance and significantly reduced side effects. However, efficacy of local immunotherapy in children has yet not been sufficiently demonstrated. This study was performed to determine clinical efficacy of high dose sublingual swallow immunotherapy (SLIT) by a double-blind placebo-controlled study in children with grass pollen allergy using high dose allergen extracts. Methods: A total of 161 children with seasonal rhinoconjunctivitis of which, 68 had also asthma symptoms were enrolled in a multicenter double-blind placebo-controlled study for 1 year and treated on a daily basis with sublingually applied allergen drops. After 1 year all children were given treatment for another 2 years in an open-controlled setting. Symptom scores and medication were assessed during the pollen seasons with structured interviews. Applied allergen dosage, compliance, and side effects were documented by daily diary cards. Primary endpoint was a clinical index (CI) combining symptom scores with medication index. Titrated skin prick tests (SPT) and specific antibody measurements were performed each year. Results: Combining symptom with medication scores to CI was highly reliable (reliability coefficient = 0.89, standard error = 9.6%). Allergen-specific IgE- and IgG-subclass antibodies increased significantly in patients treated with SLIT indicating an activation of the immune response induced by the locally applied grass pollen extract. SPT reactivity did not change during therapy. After 1 year of SLIT in the original design we observed no significant difference in the CI between treatment and placebo analyzing all patients included in the study per intention to treat and per protocol. However, subgroup analysis in a repeated measures model revealed that patients with SLIT and severe symptoms before the beginning of treatment (CI > mean/ > 1.51) showed a significant improvement of clinical symptoms after 3 years. Conclusion: In this study SLIT was accompanied by a significant placebo effect. Efficacy of treatment could only be seen in children with severe clinical symptoms and this became clinically marked after 3 years of therapy.