Water soluble polymers or polymeric hydrogels are used to encapsulate antigen to form vaccines. The antigen is mixed with a polymer solution, microparticles are formed of the polymer and antigen, and, optionally, the polymer is crosslinked to form a stable microparticle. Preferred polymers are alginate and polyphosphazenes, and mixtures thereof. Microparticles can be administered parenterally or mucosally. For oral delivery, the microparticles are preferably fifteen microns or less in diameter, and adhere to the mucosal lining of the gastrointestinal tract, increasing uptake by the reticuloendothelium.