The invention relates to a vaccine adjuvant which based on the 100% mass thereof comprises between 10% and 95% of a mineral oil containing: between 0.05 mass % and 10 mass % hydrocarbon chains having less than 16 carbon atoms and between 0.05 mass % and 5 mass % hydrocarbon chains having more than 28 carbon atoms. In addition said adjuvant has a P/N ratio corresponding to the ratio of the mass quantity of the paraffinic hydrocarbon chains to the mass quantity of the naphthenic hydrocarbon chains of between 2.5 and 3 said adjuvant being intended for the production of a vaccine composition to prevent coccidiosis.
