The molecular biology of poliovaccines

National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3QG, U.K. The molecular biology of the live attenuated Sabin vaccine strains of poliovirus has been studied extensively, and surprisingly few mutations are required to account for the greater part of the attenuated phenotype. The viruses are clearly capable of extremely rapid, extensive and precise variation in the vaccinee to adapt from the attenuated form to a form able to grow successfully in the host, yet despite this they cause almost no disease. The high degree of genetic variation in the face of general phenotypic stability in the wild-type suggests that polioviruses are extremely well adapted to their hosts and that vaccines exploit some aspects of the virus host ecology to be safe and effective. The precise mechanisms by which they do so raise possibilities of improving vaccine production and testing methods, and designing better vaccine strains.