Background:  A 3‐year course of specific immunotherapy (SIT) in children with hay fever to grass and/or birch pollen significantly reduced the risk of developing asthma. To investigate the long‐term preventive effect, we performed a follow up – 2 years after termination of immunotherapy.

Methods:  A total of 183 children, aged 6–14 years with grass and/or birch pollen allergy could be investigated 2 years after discontinuation of SIT or no treatment. Conjunctival provocation tests (CPTs) and methacholine bronchial provocation tests were carried out during the season and winter after 5 years. The development of asthma was assessed by clinical evaluation.

Results:  The significant improvement in hay fever and CPT results observed after 3 years of SIT persisted at the 5‐year follow‐up. No difference in bronchial responsiveness to methacholine was found after 5 years because of spontaneous improvement during the follow‐up period in the control patients. The immunotherapy‐treated children had significantly less asthma after 5 years as evaluated by clinical symptoms [odds ratio 2.68 (1.3–5.7)] in favor of SIT for prevention of development of asthma and significantly less patients reported an increase in asthma scores (P < 0.01).

Conclusion:  Immunotherapy for 3 years with standardized allergen extracts of grass and/or birch shows long‐term clinical effect and preventive effect on development of asthma in children with seasonal rhinoconjunctivitis.