LIVE POLIO IRUS VACCINES

Laboratory Investigations of Attenuated Poliovirus Vaccine Strains
91
scribed in detail in our report to the First Conference.l
Each section, as reported previously, has been
evaluated individually and the lesions graded
as minimal, mild, moderately severe, or severe.
Since there has been much discussion of grading
systems and many attempts at quantitation
of lesions 4,, a description of our grading system
and a discussion of its usefulness is presented.
A severe lesion is one in which the neurons
of both anterior horns of the spinal cord section
or of the motor nuclei affected in the
brainstem sections are totally or almost totally
involved.
A moderately severe lesion is one in which
(1) the extent and degree of neuronal damage
is not as great as in the first group, is present
in both the hemisections of the cord or in all
the brainstem nuclei affected, or in which (2)
the involvement may be severe but confined
only to one hemisection of the cord, or to only
several of the brainstem nuclei that might be
affected.
A mild lesion is one in which there are only
a few neurons damaged in one or both hemi-
TABLE 2.
NEUROVIRULENCE
FOLLOWING INTRAMUSCULAR INOCULATION
TYPE 1 ATTENUATED POLIOVIRUS
OF RHESUS MONKEYS WITH
Inoculum-P.F.U.
Histopathology
Clinical Lumbar Cervical B.S.
Signs
Koprowski Type I
108.7-10 8 .9 .-
107'7-107.9 2/4* 2/4 1/4 2/4
106.7-107.2 0/12 1/1z 1/12 1/12
106.2_106.4 0/2 0/2 0/2 0/2
Lederle Type I
108-7_108.9 4/4 4/4 4/4 4/4
107'7-107.9 5/14 9/14 9/14 9/14
106.7-107.2 0/4 0/4 0/4 0/4
106. 2 .106.4 .
Sabin Type I
108.7-108.9 0/4 3/4 0/4 0/4
107'7-107.9 0/14 5/14 2/14 1/14
106.7-107.2 0/4 0/4 0/4 0/4
106.2106.4 _ _ _
* No. of monkeys having findings/No. inoculated.