Confined field trial of a double recombinant vaccinia-rinderpest vaccine in Kenya: I. Determination of the minimum immunising dose in African Zebu cattle

Abstract

Twenty cattle vaccinated with doses ranging between 103 pfu and 107 pfu of a double recombinant vaccinia-rinderpest vaccine expressing the fusion (F) and haemagglutinin (H) proteins of rinderpest virus, were challenged after 28 days with a lethal dose of the virulent Kabete '0' strain of rinderpest virus. All animals vaccinated with 105, 106 and 107 pfu of the recombinant virus were fully protected against clinical signs of rinderpest. One of four cattle in each of the groups vaccinated with 103 or 104 pfu and five unvaccinated control animals developed clinical signs of the disease and died within 8-16 days of challenge. All surviving cattle vaccinated with 107 pfu of the recombinant virus did not develop anamnestic antibody responses following challenge while two out of four animals vaccinated with 106 pfu and all those vaccinated with 105 pfu or less developed anamnestic responses of four-fold or greater. The results indicated the potential value of the double recombinant vaccinia-rinderpest vaccine for immunising cattle in the field.