1. A method of protecting an animal against a chronic disease, the disease being caused by an infectious organism which undergoes more than one life cycle comprising: a) administering to the animal a vaccine containing sufficient organisms to develop an immunological response in the animal; b) maintaining the animal free from chemotherapeutic agents effective against the infectious organism for a period of time corresponding to about one life cycle of the organism; and c) thereafter administering to the animal a chemotherapeutic agent effective against the infectious organism for a period of time corresponding to at least one life cycle of the infectious organism. 2. A method as claimed in claim 1 wherein the animal is selected from the group consisting of poultry or swine. 3. A method as claimed in claim 2 wherein the animal is maintained free from chemotherapeutic agents effective against the infectious organism for a period of time corresponding to about two to five days beyond one life cycle of the organism. 4. A method as claimed in claim 3 wherein the chemotherapeutic agent effective against the infectious organism is administered to the animal for a period of time corresponding to about 1.5 to 2.5 life cycles of the infectious organism. 5. A method of protecting poultry birds against coccidiosis comprising: a) administering to the bird a vaccine containing sufficient live oocysts of at least one Eimeria spp. to develop an immunological response in the bird; b) maintaining the bird free from chemotherapeutic agents effective against coccidiosis for a period of time corresponding to about one life cycle of the Eimeria spp.; and c) thereafter administering to the bird a chemotherapeutic agent effective against coccidiosis for a period of time corresponding to at least one life cycle of the Eimeria spp. 6. A method as claimed in claim 5 wherein the bird is maintained free from chemotherapeutic agents for a period of time corresponding to about two to five days beyond one life cycle of the Eimeria spp. 7. A method as claimed in claim 6 wherein the chemotherapeutic agent is administered to the bird for a period of time corresponding to about 1.5 to 2.5 life cycles of the Eimeria spp. 8. A method as claimed in claim 5 wherein the bird is being administered with a vaccine containing sufficient live oocysts, with live cycle which is less than 10 days wherein said bird is maintained free from chemotherapeutic agents for about 10 days. 9. A method as claimed in claim 8 wherein the chemotherapeutic agent is administered to the bird for about 10 to 14 days. 10. A method as claimed in claim 9 wherein the chemotherapeutic agent is selected from the group consisting of monensin, narasin, lasalocid, samduramicin, salinomycin, laidlomycin, nigericin, grisorixin, dianemycin, lenoremycin, lonomycin, antibiotic X206, albroixin, septamycin, antibiotic A204, etheromycin, isolasalocid, antibiotic A23187, maduramicin, amprolium, diclazupil, clopidol, decoquinate, nicarbazin, robenidine, halofuginone, and zoalene. 11. A method as claimed in claim 10 wherein the chemotherapeutic agent is selected from the group consisting of monensin, narasin, lasalocid and salinomycin. 12. A method as claimed in claim 11 wherein the Eimeria sp. is one or more species selected from the group consisting of Eimeria tenella, Eimeria necatrix, Eimeria acervulina, Eimeria maxima, Eimeria brunetti, Eimeria proecox, and Eimeria mitis.