Evaluation of the placebo effect in the trials of allergen immunotherapy effectiveness: meta-analysis of randomized and placebo-controlled trials

Introduction
The total effect of the method of treatment is composed of its specific activity depending on its impact on the disease mechanism and the non-specific activity, i.e. the placebo effect. Many methods of treatment make use of such an inflammatory action.

Aim
To assess the placebo effect in the overall result of the specific immunotherapy and the analysis of its dependence on the type of specific immunotherapy, the disease, the age of a patient, the type of allergy, indicators used (objective and subjective), in patients with allergic diseases – asthma, allergic rhinitis and/or allergic conjunctivitis.

Material and Methods
A systematic review of Medline database was conducted using the EntrezPubmed search engine to find randomized placebo-controlled trials evaluating the effectiveness of specific immunotherapy in the treatment of asthma, allergic rhinitis and/or allergic conjunctivitis. After determining the contribution of the placebo effect for each of the test subjects, the calculation involved the average share of the placebo effect depending on the type of specific immunotherapy used, the type of disease, the age of the test subject, the type of allergy and the used measures of their effectiveness.

Results
The share of the placebo effect in the overall specific immunotherapy effect amounted to 39% and was comparable in the analyzed disease entities. A significantly higher share (p < 0.01) of 68% of the placebo effect in adult patients treated with sublingual immunotherapy vs. 29% in adult patients treated with subcutaneous immunotherapy.