RESUMEN
The use of vaccinia virus vector for the delivery of antigens was first described by Moss and Paoletti and their colleagues in 1982. Such vaccines could be of particular value in developing countries because they would be cheap, stable, easy to administer and provide long-lasting immunity. WHO recognized the potential value of such a delivery system by convening two meetings, one at the National Institutes of Health, USA in November 1984 and the second at WHO headquarters, Geneva, Switzerland in September 1985, to discuss the possibility of using such products, particularly with regard to their safety. Since that time, other vehicles which could be useful for the delivery of antigens have been described. These include Escherichia coli, Salmonella typhimurium, BCG, all other poxviruses, adenovirus, herpesvirus and poliovirus. At its meeting in July 1988, the Scientific Advisory Group of Experts of the Programme for Vaccine Development (SAGE) concluded that it was appropriate to discuss the general topic of live vectors and proceeded to arrange a meeting to discuss the present position and to prepare a report on the following key issues: requirements for safety and efficacy; immunological factors which may influence efficacy; medical constraints on use. The present report results from a meeting held in Geneva from 19 to 22 June 1989.