Effects of an inactivated and a modified live BVDV vaccine on amount and stability of the BVDV-antibody-titre and on protection against fetal infection - a field study

In a beef suckler production system with a previous bovine viral diarrhoea virus (BVDV) infection history numerous persistently infected (PI) calves were born in spite of vaccination with an inactivated vaccine. A modified live BVDV vaccine was therefore included in the vaccination scheme. Two study groups were formed. Animals of the field virus group (FG) (36 animals) had already born a PI calve. Animals of the negative group (NG) (30 animals) were chosen because they had had little contact to PI calves before. BVDV-antibodies were determined twice before and twice after using modified live vaccine by ELISA and quantified by serum neutralization test (SNT) against the virus strain isolated in the livestock. Animals with SN titres above 200 ND50 were defined as "protected", animals below as "not safely protected" (according to Wolf, 2012). At all times, at least 97% of FG-animals were protected. Only 16.7% of NG-animals were protected even after multiple applications of inactivated vaccine. After using the modified live vaccine the percentage of protected animals increased significantly up to 56.7% and remained around this level ten month later. By ELISA, gps in the vaccination derived protection were only seen after vaccination with the inactivated vaccine. The difference between animals protected by the modified live vaccine and by natural infection was also statistically significant. Though many animals had contact to two overlooked PI calves during their first pregnancy after vaccination with the modified live vaccine, no new PI calves developed. The results show that modified live vaccine can induce high and stable SN titres and effective fetal protection at livestock-level. A modified live vaccine should therefore be part of any BVDV-vaccination scheme.