Assessment of the viral RNA sequence heterogeneity for control of OPV neurovirulence

By using sensitive mutant analysis by PCR and restriction enzyme cleavage we have found that among several positions that differ between the wild-type and attenuated type 3 poliovirus genomes, only two positions, 472 and 2493, showed variability in vaccine lots. Of these two, only position 472 correlates with neurovirulence in monkeys, while the abundance of revertants at position 2493 indicated the type of seed virus and the passage level. Conditions of cell culture influence the rate of mutant selection, suggesting that some cellular factor(s) may be involved in selection of 472-C. Determination of 472-C content predicts which vaccine lots would fail the monkey neurovirulence test. These results imply that the PCR method can be used for optimization of manufacturing conditions.