LIVE POLIO IRUS VACCINES

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TABLE 1.
Safety-Laboratory Evidence of Attenuation and Safety
FORMULA FOR EVALUÁTION OF RELATIVE MONKEY NEUROVIRULENCE, OR DEGREES THEREOF,
AFTER INTRACEREBRAL INOCULATION
GRADE
O
CRITERIA
NO LESIONS OR TRACK LESION W/LOCAL
INFLAMMATORY REACTION
1 SIGNIFICANT INFLAMMATORY & NEURONAL
CHANGES HOMOLATERAL TO TRACK
2 LESIONS IN BRAIN STEM
3 LESIONS IN BRAIN STEM & SPREAD TO
CERVICAL OR LUMBAR CORD
4 SPREAD TO ALL PORTIONS OF THE CNS
grades 3 and 4 was 21 per cent for Type 1, 57
percent for Type 2, and 16 per cent for Type 3.
Thus, a base line of normally expected neurovirulence
for each type of Lederle polioviruses was
established as a reference for recognizing a
vaccine lot with increased activity in monkeys.
As summarized in Table 2, 4 of 12 tests performed
on 10 Type 1 lots of vaccines, 3 of 7 tests
on 6 Type 2 lots, and 5 of 10 tests on 5 Type 3
lots were above average. It must be emphasized,
however, that the animals were inoculated with
very large doses of virus (from over 105 to over
107 TCD 50 ); that most reactions occurred at 107
and 106 levels except for Type 2 virus; and that
the paralyses or weaknesses observed were nonprogressive
and non-fatal. In contrast, with much
smaller doses of virulent polioviruses, sometimes
only a few TCD 0 ,,, close to 100 per cent of animals
showed not only severe histo-pathological
changes but also developed progressive paralysis
and died of the disease 5 to 10 days following
inoculation.
Some variation was observed between two consecutive
tests with the same lot of vaccine (Table
2). For example, Type 1 tests Nos. 2 and 3 were
obtained at two different times on the same lot
TABLE 2. PARALYTIC RATES AND DEGREES OF HISTOLOGIC LESIONS OF LEDERLE STRAINS OF POLIO-
VIRUS VACCINE IN SUCCESSIVE LOTS
TEST NO.
1 2 3 4 5 6 7 8 9 10 11 12 Av.
TYPE I
PARALYTICRATE ) 13 0 1 0 0 144 4 0 0 015 8
HISTOL.LESIONS (%) 32 L 5 21 0 10 10 0 1j 6 13 26 50 21
TYPE II
PARALYTIC RATE (%) 0 0 0 0 50 13 2
HISTOL.LESIONS (%) 45 54 30 70 3 5 65 57
TYPE III
PARALYTIC RATE (%)
HISTOL.LESIONS (%)
5 0o 0 0 27 -0 10 0 29 0 6
5
0 0 0 36 16 25 20 20 0 16
Underlined figures denote pools showing above average neurovirulence.
Brackets indicate results of duplicate tests on the same vaccine lot.