Attenuation and reversion of the Sabin vaccine strains of poliovirus.

Studies of the molecular basis of the attenuation and reversion of the attenuated phenotype of the Sabin vaccine strains suggest that few mutations are involved. It is striking that mutations in the 5' non-coding region within a 10 base region implicated in a base pair structure have been identified in all the Sabin vaccine strains. The mutations have effects on in vitro phenotypes which have implications for the production of vaccines.