A vaccine adjuvant which, based on the 100% mass thereof, includes 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, the 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, the adjuvant being intended for the production of a vaccine composition to prevent coccidiosis.
