This study investigated the benefit of Bet v 1 contiguous overlapping peptide immunotherapy persists during first follow-up season. One hundred ninety-six of 240 randomized subjects for a second birch pollen season was evaluated with COP 50 mg , COP 100 mg and placebo group. Bet v 1-specific IgG4 increased by 10-20-fold after Bet v 1 COP treatment and remained elevated during the first birch pollen season. In conclusion, this study present the first successful phase IIb AIT trial based on COP reporting significant persistent clin. improvement extending to at least 2 seasons posttreatment in subjects allergic to birch pollen.