Randomised controlled trials (RCTs) of children aged up to 18 years with allergic rhinoconjunctivitis that compared immunotherapy with placebo or symptomatic treatment, or those which compared different administration forms of immunotherapy, were eligible for inclusion. RCTs that compared different doses of the same product were not eligible. To be included, studies had to report sensitivity to the administered allergen confirmed by either a positive skin test and/or serum allergen-specific IgE (immunoglobulin E). Outcome inclusion criteria were at least one of a rhinoconjunctivitis symptom score, an anti-allergic medication score and/or a composite symptom-medication score.
In the included studies, the children were aged between three and 18 years. Where stated, between 31 per cent and 88 per cent of the participants were male; overall, more boys than girls were included. Immunotherapy was subcutaneous, nasal, oral or sublingual. Treatment lasted from one to 36 months. Most studies were placebo-controlled, although some compared immunotherapy to symptomatic treatment and one of the included studies was a comparison of oral immunotherapy to subcutaneous immunotherapy. The main allergen was grass pollen (other allergens used were: house dust mite, olive pollen, mould, ragweed pollen, birch pollen or parietaria pollen).
Two reviewers independently performed the study selection. Disagreements were resolved by consensus.