Public Health Aspects of Current Oral Rabies Vaccines

Although the efficacy of the oral administration of live Street Alabama Dufferin (SAD) rabies virus for the vaccination of foxes has been proven, its use in natural settings remains controversial. Investigators have had to face three major and absolutely new problems: (1) The use in nature of a virus that has a wide range of hosts may be dangerous. Although the potential transmitters of rabies in nature are restricted to the families Canidae, Felidae, Mustelidae, and Viverridae and the order Chiroptera, it is theoretically possible that practically all species of mammals could become infected by the vaccine virus. This is a major concern with respect to safety and surveillance. (2) It is difficult or impossible to test all of the pathogenic and epidemiologic properties of the vaccine under laboratory conditions; i.e., the ecologic conditions of the field and the means of exposure to and transmission of the vaccine virus strain cannot be simulated in the laboratory. (3) There may be interference with measures that were developed for the prevention and control of overt disease and that may not be applicable when the disease is masked by inapparent infections. Between 1972 and 1977 these problems were studied as thoroughly as possible by at least 15 teams of scientists in nine countries; these efforts were coordinated by consultations with the World Health Organization (WHO). Nevertheless, it was difficult to find unequivocal answers to all the questions raised concerning the safety of the use of vaccine in the field.