A Cochrane review included 88 studies with a total of 3 792 subjects (3459 with asthma). Of the trials 42 were of immunotherapy for house mite allergy, 27 for pollen allergy, 10 for animal dander, 2 Cladosporium mould allergy, 2 latex and six trials looking at multiple allergens. Overall, there was a significant reduction in asthma symptoms and medication and improvement in bronchial hyper-reactivity following immunotherapy. There was a significant improvement in asthma symptom scores (standardised mean difference –0.59, 95% CI –0.83 to –0.35). NNT to avoid one deterioration in asthma symptoms was 3 (95% CI 3 to 5) and to avoid one requiring increased medication NNT was 4 (95% CI 3 to 6). Allergen immunotherapy significantly reduced allergen specific bronchial hyper-reactivity, with some reduction in non-specific bronchial hyper-reactivity as well. There was no consistent effect on lung function. If 16 patients were treated with immunotherapy, one would be expected to develop a local adverse reaction. If nine patients were treated with immunotherapy, one would be expected to develop a systemic reaction (of any severity).
Another systematic review including 43 rhinitis studies with a total of 2,001 subjects and 25 asthma studies with a total of 726 subjects was abstracted in DARE. Nine of thirteen studies on ragweed allergy and 14 of 15 studies on grass-pollen allergy proved efficacy. Six of nine studies on other pollen allergy proved efficacy. In the 43 rhinitis studies no efficacy was documented in 10 studies, low efficacy in 13 studies, moderate efficacy in 14 studies and high efficacy in 6 studies. Th emean clinical improvement was a 45% reduction in symptom/medication score compared with placebo. The best results were obtained in grass-pollen allergy. Three of five studies on cat and/or dog immunotherapy documented a reduction in challenge test or improvement in exposure tests. The efficacy of immunotherapy in many studies was higher than for results obtained by antihistamines (one study) and equivalent to the reduction in clinical symptoms obtained by standard doses of intranasal or inhaled corticosteroids (7 studies).