Poliovirus vaccination: current understanding of poliovirus interactions in humans and implications for the eradication of poliomyelitis.
Poliomyelitis is a paralytic disease of the motor neurones of the central nervous system, which is caused by poliovirus. The virus is transmitted by the faecal-oral route, and if virus replication is confined to the gut, it is harmless. Poliomyelitis is an ancient human disease, but was rare until the beginning of the 20th century, when children began to be exposed to the virus at older ages and were, therefore, no longer protected by maternal antibody, which had already been lost. Inactivated polio vaccines are increasingly being used in those countries in which poliomyelitis has been brought under control; however, live vaccines are still the most widely used types and the World Health Organization (WHO) have set the goal of using such vaccines to eliminate the wild-type virus throughout the world by the year 2000. Substantial progress has been made to this end; however, the strains of poliovirus that are used as vaccines are able to adapt rapidly to the human gut, losing their attenuated (weakened) character within a few weeks. Currently, there is urgent debate about the best method of stopping vaccination against poliomyelitis once the wild-type poliovirus has been eliminated completely, so that the vaccine-strain virus will also be eliminated. Proposed strategies include the abrupt cessation of vaccination with the live virus worldwide, followed by the optional use of inactivated vaccines for an appropriate period. Further information about both the epidemiology and the pathogenesis of the disease is required before an informed choice can be made. The topics covered in this article include a brief history of studies of the disease, its pathogenesis and its control by vaccination, the molecular biology of the live vaccines, which have been extremely successful in controlling poliomyelitis so far, and the concerns that are raised as the eradication of the wild-type virus approaches.
Division of Virology, National Institute for Biological Standards and Controls (NIBSC), Blanche Lane, South Mimms, Potters Bar, Hertfordshire, EN6 3QG, UK. pminor@nibsc.ac.uk
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