The protective effectiveness of an inactivated bovine ephemeral fever virus vaccine.

Bovine ephemeral fever (BEF) is an important viral disease of cattle. Despite the extensive use of inactivated vaccines for the prevention of BEF, a controlled study of their field effectiveness has never been performed. We conducted a large field effectiveness study of a BEF inactivated vaccine, during a large BEF outbreak. Neutralizing antibody titers measured in 385 heifers and calves 1 month after 2(nd) vaccination averaged 1:91.8 (CI95%=76.6-110). The effectiveness study enrolled 2780 cows in nine herds. In two herds cows vaccinated twice, 1 year before the outbreak and once 2-3 months before outbreak onset were compared with non-vaccinated cows. Average vaccine effectiveness of three vaccine doses compared to no vaccination was 47% (CI95%=34-57) in these herds. In two other herds cows vaccinated twice 1 year before the outbreak and twice again 2-3 months before outbreak were compared with cows vaccinated only twice 2-3 months prior to the outbreak. Average vaccine effectiveness of four doses compared to two doses was 49% (CI95%=25-65) in these herds. In five herds cows vaccinated twice 2-3 months before outbreak onset were compared with non-vaccinated cows. This vaccination schedule was shown to be non-effective (average effectiveness=2%, CI95%=-14-17). Milk production analysis on one of the effected herds, in which 56% vaccine effectiveness and an absolute reduction of 27% in morbidity were documented, revealed a net milk production loss of 175.9kg/sick cow (CI95%=127.9-223.9) and an average gain of 37kg for each vaccinated cow (CI95%=-3.6-77.7). This study indicates that despite the fact that two vaccine doses of the tested inactivated vaccine elicited high titers of neutralizing antibodies, partial protection was induced only when at least 3 doses were administrated before natural challenge.