LIVE POLIO IRUS VACCINES

Large-Scale Field Trial with Oral Cox-Lederle Vaccine in Dade County 443
1 were 285/300, or 95 per cent, Type 2, 152/194,
or 78 per cent, Type 3, 380/391, or 97 per cent;
and the conversion rates to titers of 1:16 or
greater were 89, 61, and 87 per cent, respectively.
In total, 817 of 885, or 92 per cent, of the antibody
gaps were filled. Forty-two of the 68, or
62 per cent, of the failures were to Type 2.
Time does not permit discussion of the more
detailed data tabulated in Tables 10-12, showing
the gross and higher titer conversion rates
by type for the various possible combinations
of serologic gaps.
We have found only 61 "triple negatives" in
approximately 2,500 individuals already tested.
None were found among individuals who had
received three or more Salk injections, and only
four in individuals who had received one or two
Salk injections. Although the highest percentage
was in the youngest age group due to
the method of sample selection, a significant
number (30) was found in young adults (Table
13). Although only 32 of 61, or 52 per cent of
"triple negatives" developed antibodies to all
three types, the Types 1 and 3 components of the
oral vaccine still showed approximately 90 per
cent efficacy in producing serologic conversion.
Thus, the gross conversion rates were: for Type
1, 54/61 (88 per cent); for Type 2, 38/61 (62
per cent), and for Type 3, 55/61 (90 per cent).
The conversion rates to titers of 1:16 or greater
were 84, 38, and 64 per cent, respectively.
Twenty-three of the 36, or 64 per cent of the
failures, involved the Type 2, either singly or
in combination.
DISCUSSION
We believe that the preliminary data reported
by us at this Conference strongly suggest that
valid large-scale field trials of oral polio vaccine
can and should be conducted in the social,
geographic, and age groups in which its ultimate
utilization is planned. Although it is more difficult
to accumulate large numbers of "triple negatives"
from the population of communities where
widespread killed polio vaccine programs have
been carried out, this problem is no different
than that which develops in areas of limited Salk
utilization when monovalent or bivalent oral
vaccine is given, for this results in conversion
of many "triple" to "double" or "single negatives",
thus leaving varying but much smaller
numbers of "triple negatives" to be challenged
by the next type given. In either case, great
reliance for vaccine testing will have to be placed
on the results with less desirable but available
"single" and "double negatives".
We deliberately selected the three-to-fourweek
interval in order to most accurately determine
the primary antigenic potency of the vaccine,
for longer intervals between feeding and
repeated bleeding would have progressively increased
the perhaps significant importance of
unmeasurable variables, such as secondary
spread of vaccine virus and spread of "wild"
TABLE 13. PoLOVmRUS ANTIBODY RESPONSE OF 61 INDIVIDUALS LACKING MEASURABLE ANTIBODIES
TO ANY TYPE OF POLIOVIRUS FED 2 ML. OF TRIVALENT ORAL POLIOMYELITIS VACCINE
POST-FEEDING TITERS
PRE-FEEDING
TRIPLE NEGATIVES