LIVE POLIO IRUS VACCINES

Laboratory Investigations of Attenuated Vaccine Strains
131
a single monkey-kidney cell culture passage may
radically alter the T character of a virus strain.
With this in mind two original filtered 10 per
cent stool suspensions of Lederle Type 1 virus
from subject J.S. were inoculated directly into
the spinal cord of Rhesus monkeys. As is illustrated
in Fig. 10, the virus in the 13 and 14 day
stools manifested a markedly increased ability
to grow at 40 ° C., and also exhibited a markedly
increased paralytic rate and a decreased histopathologic
threshold value.
The prime objective of these continuing studies
is to determine the stability of the monkey neurovirulence
character of vaccine strains in the
course of human passage. The results to date
indicate that: (a) the T character, as determined
in a plaque system, is very often, but not invariably
correlated with monkey neurovirulence; (b)
laboratory manipulation of vaccine virus or excreted
virus frequently results in rapid alteration
of T character and monkey neurovirulence, indicating
the importance of studying the virus directly
in vaccine or stool specimens; (c) virus in,
or derived from, stools of persons fed vaccine
virus exhibits a high frequency of increased
ability to propagate at 40 ° C., and increased
monkey neurovirulence.
ACKNOWLEDGMENTS
The authors wish to acknowledge the excellent
technical assistance of Mr. Marshall Ford, Mrs.
Dorothy S. Hughes, Mr. Richard J. Low, and
Mr. George Rustin.
REFERENCES
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