Inactivated African horse sickness virus cell culture vaccine.

Immunogenic killed vaccine against African Horse Sickness can be prepared from a neurotropic vaccine strain or a virulent strain of virus, type 9, grown in a monkey kidney stable cell line. Virus was inactivated with either formaldehyde in a final concentration of 1:8000 or β-propiolactone at 0·2 per cent. In order to enhance the immunogenicity of the product, aluminium hydroxide was added to the vaccine as an adjuvant. After inoculation of a single dose of either vaccine, neutralizing antibodies developed with 4 weeks, and all horses resisted challenge with homologous virulent virus. When two injections of inactivated vaccine were administered at an interval of 4 weeks, much higher neutralizing antibodies were present in sera and 6 months later all horses were still resistant to a challenge dose of virulent virus. Under the conditions of these experiments a significantly higher degree of antigenicity was demonstrated with formalin-inactivated vaccine than with β-propiolactone-inactivated vaccine.