Clinical Outcomes in Placebo-Injection and Injection-Free Cohorts in Birch Pollen Allergy: An Exploratory Cross-Study Comparison.

Background/Objectives: Placebo responses can complicate the interpretation of allergen immunotherapy (AIT) trials because symptom- and medication-based outcomes may be influenced by the trial context in addition to treatment-specific effects. Injection-free comparison cohorts are rarely available in conventional double-blind, placebo-controlled AIT trials. We therefore conducted an exploratory post hoc cross-study comparison of clinical outcomes in two placebo-injection cohorts and an injection-free cohort of birch pollen-allergic participants. Methods: Data from three prospective clinical studies evaluating the mannan-conjugated birch pollen allergoid EP-088-T502-T502-SIT-020, T502-SIT-045, and T502-SIT-068-were assembled for this cross-study comparison. Placebo-injection cohorts from studies T502-SIT-020 and T502-SIT-045 were compared with the injection-free cohort from study T502-SIT-068. Clinical outcomes included the Combined Symptom and Medication Score (CSMS), daily Symptom Score (dSS), and daily Medication Score (dMS). Results: The primary peak-period analysis included 60, 93, and 160 participants from T502-SIT-020, T502-SIT-045, and T502-SIT-068, respectively. During the site-specific 14-day peak birch pollen periods, median CSMS was 2.14 in the injection-free cohort compared with 1.34 and 1.07 in the T502-SIT-020 and T502-SIT-045 placebo-injection cohorts, respectively. These values corresponded descriptively to approximately 37% and 50% lower cohort medians, respectively, relative to the injection-free cohort. Median dSS, which was defined consistently across the three source studies, was 1.22 in the injection-free cohort compared with 0.78 and 0.70 in the two placebo-injection cohorts. Median dMS was 0.93 compared with 0.39 and 0.36, respectively. The same between-cohort pattern was observed in the secondary fixed 1-30 April analysis. Conclusions: Both placebo-injection cohorts showed lower CSMS and dSS values than the injection-free cohort. Because the cohorts were non-concurrent and derived from separate studies, the observed differences do not establish a causal effect of placebo injections.