A method for obtaining an immunogenic strain useful for producing a vaccine against Coccidiosis comprises the cycle of infecting at least one first group of specific pathogen-free donor birds with oocysts from an Eimeria species. Blood is then collected from these donor birds, and is then used to infect a second group of specific pathogen-free birds. Oocysts are collected from the second group of birds. These oocysts are then multiplicated to complete the cycle. The cycle is then repeated using the multiplicated oocysts. After a total of about three cycles, a final antigen may be harvested and utilized as a source to generate oocysts for a vaccine.