ABSTRACT
The genetic stability of the three Sabin oral poliovaccine (OPV) strains produced on either primary monkey kidney (VK) or Vero cell substrates was compared in vivo and in vitro by measuring the rate at which the bases most strongly associated with attenuation and reversion to neurovirulence (positions 480, 481, and 472 in the 5' non-coding region of Sabin 1, 2 and 3 respectively, and 2034 in VP3 of Sabin 3) reverted during passage of the vaccine strains in the gastrointestinal tract of primary vaccinees and in cell culture. For the in vivo study, the poliovirus excretion patterns of 21 infants receiving OPV produced on either VK or Vero cells were followed for 21 days. No significant differences in either the frequency of excretion or the rate of reversion were observed between the two vaccine groups. The rate of accumulation of revertants during passage in vitro was compared for the three Sabin strains passaged 10 times in either VK or Vero cells. For types 1 and 3, revertants accumulated faster upon passage through VK cells compared with passage through Vero cells. Type 2 appeared to be stable as no revertants were detected in either cell type. Results of this study suggest that the use of Vero as opposed to VK cells as substrate for the manufacture of OPV does not negatively influence the genetic stability of the three Sabin OPV strains in vivo or in vitro.
