The assessment in sheep of an inactivated vaccine of parainfluenza 3 virus incorporating double stranded RNA (BRL 5907) as adjuvant.

The serological responses of conventionally reared sheep were compared after vaccination with inactivated parainfluenza 3 (PI3) virus incorporated in three different adjuvants. Inactivated PI3 virus with the double-stranded RNA, BRL 5907 in an oil emulsion was shown to stimulate higher serum antibody titres over the first 5 weeks after vaccination than virus with and without BCG emulsified in oil. The ability of this vaccine to protect specific pathogen-free lambs against challenge with PI3 virus was examined in a second experiment. In this experiment the vaccine stimulated virus neutralizing and haemagglutination inhibiting antibodies in the serum. After intranasal and intratracheal inoculation with PI3 virus at challenge, vaccinated lambs showed no clinical illness and virus isolation was confined, except in one lamb, to the first two days. In contrast, unvaccinated lambs developed respiratory disease and virus was isolated daily for 7 days after challenge.