Problems Associated with the Use of Live Poliovirus Vaccine

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Abstract
This paper is concerned with the question of the genetic stability of the live attenuated poliovirus vaccines which are being tried now in the field in many parts of the world. A significant proportion of vaccinated children excrete viral progeny which show an increase in monkey spinal neuro-virulence over that in the vaccine. Data obtained by the intraspinal route were severely criticized on the assumption that the associated traumatic damage in the cords could account for the high rate of paralysis observed in intraspinally inoculated monkeys. New intramuscular data indicate clearly that viruses which are recovered from vaccinated children and which show changes in certain of their in vitro genetic characters show concomitant increases in their neurovirulence for the monkey, even when inoculated by a peripheral route which deposits the virus far from the site of the lesion in the central nervous system. Even under ideal circumstances of mass administration of the live vaccine, data are already available to show that mass immunization is not always an inevitable response. The reason for this is discussed in this report, namely that a certain and variable part of the community may carry other enteroviruses which interfere with "takes" from the vaccine virus. When the enterovirus infection ceases, such individuals are apt to pick up passage virus from a vaccinated person in the community. Thus for optimal safety it is essential that the vaccine virus used does not revert towards increased neurovirulence in the course of human passage.

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