Multicenter, international, parallel-group follow-up study of subjects randomized and treated in Study AN004T (AllerT 100 µg, AllerT 50 µg, placebo) and followed over the 2nd, and if appropriate, the 3rd and 4th birch pollen seasons in this study (still double-blind during the 1st year, open-label in the 2nd and 3rd years).