Efficacy of 5-Grass Pollen Liquid Sublingual Allergen Immunotherapy for Seasonal Allergic Rhinoconjunctivitis: A Systematic Review and Meta-analysis.

The efficacy and safety of allergen immunotherapy (AIT) have been demonstrated in randomized controlled trials (RCTs). However, differences in study protocols, populations, and AIT products lead to variability in outcomes. The World Allergy Organization and the European Academy of Allergy and Clinical Immunology advise assessing individual AIT products rather than assuming a universal class effect. We conducted a meta-analysis on the efficacy and safety of 5-grass pollen liquid sublingual immunotherapy (SLIT) (5-grass SLIT-liquid) in patients affected by allergic rhinoconjunctivitis (ARC) with and without asthma. We searched computerized databases (MEDLINE, ISI Web of Science, LILACS, the Cochrane Library, ClinicalTrial.gov) up to June 2023, supplemented our approach with manual literature searches, and included RCTs comparing 5-grass SLIT-liquid to placebo, irrespective of primary endpoints or treatment duration. Efficacy was assessed based on standardized mean differences (SMDs) in symptom score (SS) and medication score (MS). Subgroup analyses included age and sensitization status, while meta-regression was applied to evaluate asthma comorbidity, dose, and treatment duration. Bias and certainty of evidence were assessed using the Cochrane Risk of Bias 2 tool and the Grading of Recommendations Assessment, Development and Evaluation approach. Data from 8 RCTs for SS (621 patients) and 6 RCTs for MS (507 patients) showed a significant benefit for SLIT over placebo in SS (SMD, -0.34; 95%CI, -0.62 to -0.06; P<.05) and MS (SMD, -0.54; 95%CI, -0.97 to -0.10; P<.05). Subgroup analyses showed no differences based on age or sensitization status. Meta-regression revealed no significant impact of cumulative dose, treatment duration, or asthma on efficacy. No safety issues were observed. This meta-analysis confirms that 5-grass SLIT-liquid offers significant clinical benefits and is safe, providing an effective option for treating the cause of ARC in patients with and without asthma.