Field trials of a recombinant rabies vaccine

Abstract

To improve both safety and stability of the vaccines used in the field to vaccinate foxes against rabies by the oral route, a recombinant vaccinia virus, expressing the glycoprotein of rabies virus (VVTGgRAB) has been developed. VVTGgRAB innocuity was verified in target species and in domestic animals as well as in numerous wild animal species that could compete with the red fox in consuming vaccine baits in Europe. Oral immunization of foxes, by distributing VVTGgRAB vaccine-baits, was undertaken for the whole infected area in Belgium (10,000 km2). Five campaigns of fox vaccination, were carried out from autumn 1989 until 1991. Each time, 150,000 vaccine-baits were dropped by air at a mean density of 15 per km2. These campaigns induced a drastic decrease in the incidence of rabies and the elimination of the disease from 80% of the initially infected area. Regarding the geographical evolution of rabies in Belgium and in adjacent regions in neighbouring countries, new spatial strategies for bait dispersal were planned for 1992, 1993 and 1994: successive confined campaigns were carried out along political borders only. These campaigns induced a new decrease of incidence; no rabid fox could be detected in 1993 in spite of an improved epidemiological surveillance. In 1994, rabies was again confirmed in 13 foxes collected in an area close to the French border. These cases demonstrated the persistence of a border rabies focus and justify further restricted vaccination campaigns.