An embodiment of the present invention features a dosage form for administering antigen to cause an immune response in an animal or human subject in the nature of a vaccine. The dosage form comprises spheres having an effective amount of antigen to create an immune response and having an average diameter of 0.01 to 10.0 microns. The spheres comprise a polymer selected from the group consisting of poly(L-lactic acid), poly(D, L-lactic acid), poly(glycolic acid) and carboxylic acid and ester derivatives thereof, poly(fumaric anhydride) and poly(sebacic anhydride) and derivatives thereof. The spheres can be lyophilized and stored as a powder prior to use. The spheres can then be reconstituted and formulated in buffers with adjuvants.
