Safety and Effectiveness of Subcutaneous Immunotherapy with an Undiluted Glutaraldehyde-Polymerized Pollen Extract Mixture in Adults and Children with Allergic Rhinitis with or Without Asthma Due to Olive and Grass Pollen

Background/Objectives: To evaluate the tolerability and effectiveness of subcutaneous immunotherapy (SCIT) with a glutaraldehyde-polymerized undiluted mixture of grass and olive pollen in adults and children with allergic respiratory disease in routine clinical practice. Methods: Observational, ambispective, controlled multicenter study including patients ≥ 5 years with allergic rhinitis/rhinoconjunctivitis +/− asthma due to olive and grass pollen. Patients initiating SCIT with Olea europaea/grass pollens undiluted mixtures were included in the O&G group, and those continuing symptomatic treatment in the untreated (UT) group. Safety (primary objective) was assessed as the incidence of adverse reactions. Effectiveness variables (symptoms, control, and medication use) were compared during the pollen season before and after AIT; patients and investigators reported perceived satisfaction. Results: We included 218 patients in the O&G group (children, 23.4%; adolescents, 13.8%; adults, 62.8%) with a mean (SD) age of 26.5 (15.6) years, and 94 in the UT group. At the time of evaluation, patients had received treatment for a mean (SD) of 10.6 (2.5) months. Seventeen patients (7.8%) experienced 18 adverse reactions in total, all local (12 in adults, 6 in children; mean overall rate: 0.8%). Rhinitis frequency shifted from predominantly persistent to intermittent (−64.6% in persistent) (p < 0.0001), with significantly improved intensity and control overall and across age groups in the O&G group but not in the UT group. Patients with asthma symptoms decreased by −46.6% (p < 0.0001), along with improved asthma classification, treatment steps, and control overall (O&G group), and across most age groups. Changes in conjunctivitis symptoms followed a similar trend. Symptomatic medication use significantly decreased overall (O&G group) and across specific age groups. Patients and investigators perceived decreased symptoms and medication use after AIT. Conclusions: SCIT with a glutaraldehyde-polymerized undiluted allergen mixture of olive/grass pollen extract demonstrated safety and effectiveness to treat allergic rhinitis and asthma in adults and children in a real-world setting.