Properties of a new attenuated type 3 poliovirus

Summary

The detailed results of neurovirulence tests of four new attenuated type 3 poliovirus variants on monkeys are presented.

The intracerebral test was negative with all the four variants, whereas all control animals inoculated with a wild virus developed paralysis.

In the intraspinal test none of the four new variants elicited a clinical illness, and the histological lesions indicated a high degree of attenuation of all the variants.

The mildest histological lesions were provoked by the USOL-D bac variant. The lesions were mild even after an intraspinal dose of 10⁷ TCD₅₀, including cases when the spinal cord had been pronouncedly traumatized. In all the animals the lesions were confined to the lumbar intumescence, so that a spread of the virus was not demonstrated.

The severity and extent of the lesions following the inoculation of the USOL-D bac virus were significantly lower than after the injection of Sabin's Leon 12a₁b strain, with the lesions elicited by Sabin's strain being comparable with the results of other laboratories.

No significant differences were observed between three successively performed series of intraspinal tests.

Safety tests with the first lot of the vaccine confirmed the high degree of attenuation. The vaccine virus did not have changed properties as compared with the seed virus.