Abstract: The present invention relates to the use of a recombinant modified vaccinia virus Ankara (MVA) comprising a heterologous nucleic acid for the production of a medicament for the prevention and/or treatment of type I hypersensitivity in a living animal including humans. The invention further relates to a recombinant modified vaccinia virus Ankara (MVA) comprising a heterologous nucleic acid, wherein the heterologous nucleic acid is incorporated into a non-essential region of the genome of the MVA, the heterologous nucleic acid is under the control of, e.g. a vaccinia virus-specific promoter and, the heterologous nucleic acid is selected from the group of nucleic acids encoding an allergen selected from the group of weed pollens, grass pollens, tree pollens, mites, animals, fungi, insects, rubber, worms, human autoallergens, and foods.