The Relationship of Pollen Dispersal with Allergy Symptoms and Immunotherapy: Allergen Immunotherapy Improves Symptoms in the Late Period of Japanese Cedar Pollen Dispersal

Background: The severity of symptoms of pollen-induced allergic rhinitis is affected by the amount of scattered pollen. However, the relationships between the pollen dispersal pattern, symptom severity, and treatment efficacy are not clear. Methods: Between 2007 and 2012, we performed 4 randomized, placebo-controlled studies of sublingual immunotherapy (SLIT) on patients with Japanese cedar-induced allergic rhinitis who lived in or around Chiba, Japan. The participants were asked to avoid using rescue medicines during the cedar pollen season as much as possible and to record their nasal symptoms in allergy diaries. The amount of pollen dispersed daily was quantified using the Durham method, and the season was divided into early and late periods based on the pollen count. Results: A total of 721 patients were enrolled in the 4 studies during the 6-year study period. In the placebo group (n = 349), a correlation was observed between the amount of pollen dispersed and the severity of symptoms in the early but not late period of pollen dispersal. Treatment with SLIT (n = 372) significantly improved symptom severity in the late but not early period. Conclusion: For patients with Japanese cedar pollen-induced allergic rhinitis, the fluctuation of daily pollen dispersal had a minimal effect on the severity of symptoms during the late period. SLIT was remarkably effective in alleviating symptoms during this period but not in the early period.