Effect of 2-year placebo-controlled immunotherapy on airway symptoms and medication in patients with birch pollen allergy

Background: Birch pollen is a common allergen in northern, central, and eastern Europe. Earlier studies of specific immunotherapy using birch pollen extract were not placebo-controlled or were only preseasonal. Long-term, placebo-controlled studies with subcutaneously administered standardized birch pollen extract are lacking. Objective: The aim of this study was to evaluate the effect of immunotherapy with birch pollen extract on airway symptoms and use of medication in adult birch pollen-allergic patients in a double-blind, placebo-controlled trial. Methods: Forty-nine patients with histories of birch pollen allergy from the upper and lower airways, positive skin prick test and conjunctival provocation test results, and in vitro specific IgE to birch pollen (Betula verrucosa) extract were included. Immunotherapy with birch pollen extract was given during 2 consecutive years in a double-blind, randomized, placebo-controlled study. Clinical symptom scores from the upper and lower airways and use of rescue medication were registered throughout the pollen season. Results: Forty-six patients reached the maintenance dose and were maintained on that dose during the 2-year study. The median symptom scores during the 1997 and 1998 seasons were 1.3 and 2.6, respectively, in the specific immunotherapy group and 2.1 and 4.3, respectively, in the placebo group. The differences between the groups were significant (P = .05 in 1997 and P = .005 in 1998). The placebo group used significantly more rescue medication during both seasons than the specific immunotherapy group (P = .004 for 1997 and P = .004 for 1998). Conclusion: Specific immunotherapy with birch pollen extract is an effective and safe treatment for reducing clinical allergy symptoms and medication use in birch pollen-allergic patients during the pollen season.