Development of candidates for new type 2 and type 3 oral poliovirus vaccines

Monkey neurovirulence tests on in vitro recombinant viruses between the virulent Mahoney and the attenuated Sabin 1 strains of type 1 poliovirus revealed that a strong neurovirulence determinant(s) resided in the 5' non-coding sequence of the genome and that the surface structure of the virion particle had a little correlation with the neurovirulence or attenuation phenotype. The results suggested that new and safer vaccine strains of type 2 and type 3 polioviruses may be constructed in vitro by replacing the sequence encoding the antigenic determinants in viral capsid proteins of the Sabin 1 genome by the corresponding sequences of the type 2 and type 3 genome, respectively, because the Sabin 1 strain is the safest vaccine among the Sabin strains. We have constructed recombinant viruses, PV1/2 (SS)BB and PV1/3(SS)BN, as vaccine candidates for type 2 and type 3 oral poliovirus vaccines respectively. These recombinant viruses were fully viable and showed antigenicities and immunogenicities identical to those of type 2 and type 3 polioviruses respectively. The monkey neurovirulence tests performed on these recombinant viruses suggest that the recombinant viruses are possible candidates for new type 2 and type 3 poliovirus vaccine strains.