Eight studies (n=343) were included: one RCT (n=108), four double-blind, placebo-controlled trials (n=131), one non-randomised controlled open study (n=28) and two open observational studies (n=76).
Only clinical outcomes (symptoms and mediation use) are reported below. The review also reported the results of skin testing.
Dust mite: one open study (20 adults and children with asthma treated with 12 to 96 months’ immunotherapy) reported a relapse rate of 55% within 3 years after immunotherapy discontinuation.
Cat and dog: one double-blind, placebo-controlled study (32 patients with dog- or cat-induced asthma treated with 3 years immunotherapy) reported 56% (17 out of 30) of patients with unchanged and 30% (9 out of 30) with improved tolerance in the 5 years since immunotherapy had been discontinued.
Grass pollen: 4 studies were identified. One double-blind, placebo-controlled study (32 patients with severe grass pollen allergic rhinitis treated for 3 to 4 years with SCIT then allocated to continued immunotherapy or placebo) reported no difference between continued immunotherapy and placebo in medication or symptom scores at 3 years. One double-blind, placebo-controlled study (108 patients with seasonal rhinoconjunctivitis treated with 3 years rye/grass pollen immunotherapy) reported an increasing number of patients with worsening symptoms in the 4 years after immunotherapy discontinuation (3% in year 1, 16% in year 2, 30% in year 3 and 33% in a subset of 67 patients at year 4). Most patients (70% of a subgroup of 40 patients) who relapsed responded to pre-seasonal booster immunotherapy. One open controlled study (28 children with allergic rhinoconjunctivitis allocated to 3 years’ grass immunotherapy or pharmacological treatment if SCIT was refused) reported that children (13 of the 14 followed up) in the immunotherapy group had significantly lower total symptom scores and individual symptoms plus combined symptom and medication scores 6 years after discontinuation of immunotherapy compared with the pharmacology treated group (10 of the 14 followed up). A high-percentage required medication for treating seasonal symptoms (69% of immunotherapy group and 80% of control group). Twelve years after immunotherapy was discontinued (12 patients in the immunotherapy group and 10 in the control group), a follow-up study reported significantly lower symptoms in the immunotherapy group and significantly fewer new sensitisations. One double-blind placebo-controlled study (38 adults treated with 2.5 years’ grass pollen immunotherapy) reported low medication and symptom scores 6 years after discontinuation of immunotherapy compared with end-of-treatment results.
Birch pollen: one open study (36 patients with asthma and rhinitis treated with 3 years’ birch pollen immunotherapy) reported that improvement was maintained in 86% of rhinitis and 68% of asthma patients, 6 years after discontinuation of immunotherapy.
Ragweed: one double-blind placebo-controlled study (28 adults with ragweed rhinitis treated with at least 3 years’ immunotherapy, then randomised to continued immunotherapy or placebo for 1 year) reported no significant difference between treatment groups in symptom scores.