Various vaccines containing the 919 strain of ephemeral fever virus were evaluated in experimental calves and in commercial cattle. The vaccine virus was mixed with one of the adjuvants, Quil A (a saponin derivative), aluminium hydroxide gel, dextran sulphate or combinations of these. The response of experimental calves was evaluated by measuring the production of neutralising antibodies and by resistance to challenge with virulent virus; the response of commercial cattle was judged only by the production of neutralising antibody. Twelve calves given two doses of vaccine containing Quil A produced neutralising antibodies to bovine ephemeral fever virus and all were resistant to challenge with virulent virus given 28 to 76 days after the second vaccination. The vaccine given in three of these calves also contained aluminium hydroxide gel. Six of eight unvaccinated control calves succumbed to experimental challenge. In commercial cattle (17 to 26 animals per group) the serological response after two doses of vaccine containing Quil A or Quil A and dextran sulphate was significantly better than that after vaccines containing only dextran sulphate or after vaccines containing combinations of aluminium hydroxide gel and Quil A. The adjuvant Quil A alone was tested in cattle and shown to produce a transient soft swelling at the injection site as well as a rise in rectal temperature of greater than 1 degree C one day after inoculation. At least 99.99 per cent of viral infectivity was destroyed when the vaccine was mixed with Quil A, suggesting that live virus may not be essential in the immunogenicity of the vaccine. This vaccine overcame two of the problems associated with previous attenuated vaccines tested in Australia; the necessity for adjuvant and virus to be mixed immediately before use and the large volume of the vaccine.
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