Infection with Eimeria coccidia induces a strong, species-specific protective immunity. As a result, several live coccidial vaccines are used in commercial poultry. These vaccines typically contain live sporulated oocysts from multiple Eimeria species and strains. Some consist of virulent, drug-sensitive organisms administered repeatedly in very low doses of oocysts (trickle infection). Some of these organisms have been attenuated by repeated passage through eggs, but this only works well for Eimeria tenella