The present study showed that the neurovirulence test for the lesioninducing virus dose in the spinal cord in 50% of monkeys inoculated with oral poliovaccine (Sabin) (LID
50) reflected to a large extent safety and efficacy of the vaccine upon administration to children. The degree of attenuation of the vaccine in terms of LID
50 appeared to be related to the decrease in the vaccine-associated cases as well as the seroconversion rate. An exceptional case, however, was noted in which lot No. 301 was not classified into less attenuated vaccine by the neurovirulence test. This fact suggests that the method we have employed awaits further improvement.
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