From The Journal of Allergy and Clinical Immunology
Within the European Union, there are major differences in Allergen Immunotherapy (AIT) products approved and used in individual countries. There are major differences in the clinical approach to subcutaneous immunotherapy in polysensitized patients.
In the United States mixed extracts containing multiple aeroallergens are used, whereas European allergists preferably administer separate injections of single allergen sources or homologous groups deemed to be clinically relevant.
Moreover, the regulatory approach differs between the European Union and United States. In contrast to the United States, where common allergen standards exist based on biologic activity, no common standards exist in Europe.