LIVE POLIO IRUS VACCINES

24
Safety-Laboratory Evidence of Attenuation and Safety
TABLE 10. NEUROVIRULENCE AND VIREMIA AFTER INTRAMUSCULAR INOCULATION OF MONKEYS WITH
VIRULENT AND ATTENUATED POLIOVIRUSES AND POLlOVIRUS ISOLATES FROM VACCINEES AND CONTACTS
* Par. = paralysis.
Wk. = weakness.
t All 12 monkeys with viremia received Type 2 P, 2 vaccine virus.
: 3 Polio-l.
* * 2 Polio-2 and 19 Polio-3.
shown in the last three columns of the table,
viremia was present on days 2, 3, and 4, being
a relatively common finding when a virulent
strain was inoculated intramuscularly into
monkeys.
The attenuated strains yielded an entirely
different picture. Of 64 monkeys in these tests,
none developed disease, and only 5 showed
lesions, all of these being mild. The pattern of
viremia was also different. Of 36 animals
studied on the second day, 12 were positive; all
12 positives were Type 2. The chief importance
of these data reside in the bottom two rows
of the table-the data pertaining to the isolates.
For the three d+T- isolates, 5 of 6 monkeys
developed disease, and all 6 animals showed
lesions in the spinal cord. For the 21 d+T+
strains, 52 monkeys were used. Seventeen developed
flagrant paralysis, 5 developed weakness,
and 26 of the animals developed lesionsan
attack rate of 50 per cent. As regards
viremia, this was a common finding on the second
day, when 33 of 50 animals were positive,
but tapered off on the fourth day, when only
7 out of 46 animals were positive.
The data on the isolates are shown in greater
detail in Table 11. In general, the pattern
was the same for the different areas-for children
fed during the winter in Houston and
Cincinnati, or from children fed in warmer
climates in Mexico. Paralysis occurred in many
of the monkeys receiving strains with changed
markers. However, a number of d+T+ Type 3
isolates failed to paralyze the injected monkeys,
although they did produce viremia and in this
way differed from the d-T- Type 3 vaccine.
Thus, genetic change as measured by reversion
in the d-T- markers to d+T+ is not always
associated with full intramuscular neurovirulence.
Other factors, as yet unknown, are apparently
also involved. This is further illustrated
in the data in Table 12, which represents
two families fed Type 3 vaccine virus in the
Fox-Gelfand study in New Orleans. The vaccinated
children in two families excreted a T-
virus on the first day and a T± virus on the
second day after the feeding, but later samples
were d+T+. The d+T- specimens from the
vaccinated children failed to produce lesions
or disease in four monkeys although all four
animals developed viremia on day 2, and three on
day 4. In contrast, d+T+ specimens from three