Methods and compositions are disclosed for vaccinating warm-blooded animals against coccidiosis utilizing suspensions of excysted coccidial sporozoites in physiologically balanced medium containing water-soluble polymeric stabilizers selected from gels, gelatins, polysaccharide gums, cellulose or cellulose derivatives which extend viability or storage, additional extension of viability in storage being attained when the suspensions are finely divided and the polymeric stabilizers are hardened to form microcapsules.