Prospective Evaluation of Symptom Burden and Medication Use in Seasonal Allergic Rhinitis/Rhinoconjunctivitis Patients Considering Allergen-Specific Immunotherapy

Background/Objectives: Allergen immunotherapy (AIT) is the only disease-modifying treatment for grass pollen allergy. However, the proportion of patients interested in AIT who meet guideline-defined eligibility criteria remains unclear. This study aimed to characterise symptom burden, medication use, and AIT eligibility in adult patients with grass pollen allergy during the peak pollen season. Methods: In this multicentre, prospective, non-interventional epidemiological study, 479 adults with confirmed grass pollen allergy recorded daily nasal, ocular, and systemic symptoms, as well as anti-allergic medication use, via a validated electronic diary (CCC STUDY Diary) over a 30-day period in June/July 2025. A combined symptom–medication score (CSMS) was calculated daily, with a predefined threshold of ≥1.5 indicating clinically relevant symptom severity and potential eligibility for AIT. Both additive and weighted calculation approaches for the CSMS and the daily medication score (dMS) were evaluated to assess methodological robustness and reproducibility. Results: The mean additive CSMS was 2.14, indicating moderate symptom burden. Overall, 63.3% of participants exceeded the CSMS threshold of 1.5 and were considered eligible for AIT. Sensitivity analyses demonstrated excellent concordance between additive and weighted CSMS/dMS calculations (Spearman’s ρ >0.98; p < 0.001), and Bland–Altman analysis confirmed minimal bias (0.157) and narrow limits of agreement. Asthma was reported as a comorbidity in 36% of patients, generally associated with mild to moderate daily respiratory symptoms. Limitations included the self-reported nature of the data and a slightly reduced sample size; however, the results are representative of adult patients seeking care in specialised allergy centres in Germany. Conclusions: The CSMS also in its additive and therefore modernised form is a reliable, reproducible, and clinically meaningful tool for quantifying symptom severity and identifying patients suitable for AIT. Approximately two-thirds of adults interested in grass pollen AIT exhibited moderate to severe symptoms and were eligible for treatment according to current guideline recommendations.