Background: Allergy immunotherapy targets the immunological cause of allergic rhinoconjunctivitis and allergic asthma and has the potential to alter the natural course of allergic disease.

Objective: The primary objective was to investigate the effect of the SQ grass sublingual immunotherapy tablet compared with placebo on the risk of developing asthma.

Methods: A total of 812 children (5-12 years), with a clinically relevant history of grass pollen allergic rhinoconjunctivitis and no medical history or signs of asthma, were included in the randomized, double-blind, placebo-controlled trial, comprising 3 years of treatment and 2 years of follow-up.

Results: There was no difference in time to onset of asthma, defined by prespecified asthma criteria relying on documented reversible impairment of lung function (primary endpoint). Treatment with the SQ grass sublingual immunotherapy tablet significantly reduced the risk of experiencing asthma symptoms or using asthma medication at the end of trial (odds ratio = 0.66, P < .036), during the 2-year posttreatment follow-up, and during the entire 5-year trial period. Also, grass allergic rhinoconjunctivitis symptoms were 22% to 30% reduced (P < .005 for all 5 years). At the end of the trial, the use of allergic rhinoconjunctivitis pharmacotherapy was significantly less (27% relative difference to placebo, P < .001). Total IgE, grass pollen–specific IgE, and skin prick test reactivity to grass pollen were all reduced compared to placebo.

Conclusions: Treatment with the SQ grass sublingual immunotherapy tablet reduced the risk of experiencing asthma symptoms and using asthma medication, and had a positive, long-term clinical effect on rhinoconjunctivitis symptoms and medication use but did not show an effect on the time to onset of asthma.