Real-world safety and clinical outcomes of cluster subcutaneous immunotherapy with olive pollen extracts, with or without grass pollen, in patients with allergic rhinoconjunctivitis and/or asthma

Background Allergen immunotherapy (AIT) is the only treatment capable of modifying the natural course of IgE-mediated allergic diseases induced by aeroallergens. Cluster schedules for subcutaneous AIT (SCIT) with hypoallergenic depot extracts enable faster dose escalation while maintaining a favorable safety profile. However, specific data on the use of Olea europaea extracts, alone or combined with grass pollen, remain limited, particularly in Mediterranean populations. Methods The OLGA study was a multicenter, retrospective, real-world analysis conducted in 16 allergy centers across Spain. Patients with IgE-mediated allergic rhinoconjunctivitis and/or asthma sensitized to Olea europaea , with or without grass pollen, received SCIT administered according to a cluster schedule. Safety and clinical outcomes were assessed over one year through physician-reported adverse reactions (ARs) and changes in nasal, non-nasal, and asthmatic symptom scores. Results Data from 245 patients were analyzed (51% male; mean age 26.6 years). ARs occurred in 27.3% of patients and were predominantly mild local reactions; no grade 3 or higher systemic reactions, hospitalizations, or treatment discontinuations due to ARs were reported. Favorable changes were observed across all symptom domains during follow-up (nasal Δ− 5.05; non-nasal Δ− 4.00; total Δ− 9.06; all p < 0.001), together with a reduction in the annual number of asthma exacerbations (Δ− 2.7; p < 0.001). The proportion of patients meeting predefined thresholds for clinically relevant change exceeded 93% across all evaluated domains. Similar outcome patterns were observed for olive-only and olive-plus-grass products. Conclusions This multicenter real-world study provides information on the safety profile and clinical outcomes observed in patients receiving depot allergoid SCIT administered in a cluster schedule. The findings contribute to the evidence describing the use of accelerated SCIT schedules in patients sensitized to Olea europaea pollen under routine clinical practice conditions.