A new inactivated BVDV genotype I and II vaccine - An immunisation and challenge study with BVDV genotype I

An inactivated vaccine containing BVDV I and II strains (PT810; BVDV I, and 890; BVDV II) and using different adjuvants and antigen dosages was tested in a cattle challenge model. Groups of six healthy, seronegative cattle were vaccinated twice with a low dose (106.6 TCID50 PT810 and 107.2 TCID50 890) vaccine with the adjuvant Bay R1005 or a high dose (107.8 TCID50 PT810 and 108.2 TCID50 890) vaccine with two different adjuvants (Bay R1005 or Polygen). Thirty-eight days after the second vaccination, immunised animals (n=18) and non-vaccinated control animals (n=3) were challenged intranasally with 106 TCID50 BVDV strain PT810. For a period of 16 days, virus was isolated from blood leukocytes and nasal swabs, and neutralising antibody titres were determined. The induction of antibodies following immunisation was strongly dependent on the antigen dosage in the vaccine. The high dose formulation induced high serum neutralising antibody titres against both genotypes of up to 32 000 after the second immunisation. Animals with neutralising antibody titres >512 (n=14) did not show any marked leukopenia after challenge and only very little or no virus could be isolated from blood leukocytes and/or nasal swabs when compared to control cattle. Furthermore, some of these animals did not show any boost of neutralising or even NS3-specific antibodies, which renders viral replication unlikely and thus would prevent infection of the fetus. Both adjuvants (Bay R1005 or Polygen) were similarly efficient and induced nearly identical antibody responses. In contrast, four of the six low dosage vaccinates had a marked leukopenia and viraemia as well as detectable nasal virus shedding for several days. We conclude that the selected strains and the system of vaccine preparation with high BVDV antigen dosages and highly efficient new adjuvants provide an effective means of protection against BVDV I infections. Investigations to demonstrate the protection against BVDV II infections, the duration of immunity and the ability of fetal protection by using the high dose vaccine in a fetal challenge model will follow.