LIVE POLIO IRUS VACCINES

146
Safety-Field Evidence of Safety
by placebo feeding to serve as indices of virus
spread (21 and 39 per cent, respectively).
Analysis of the data. The histories of Salk
vaccination were verified from official local health
records and can be considered to be quite accurate.
However, since the participating households
had not been under observation prior to
vaccination, certainty as to individual natural
immunity status often was not possible. Rather
than make arbitrary judgments in the individual
case, the children have been assigned to two
groups according to their prefeeding titer of neu-
tralizing antibody, one with no antibody or titers
below 1:32 (presumed to include chiefly the
natural susceptibles) and the other with titers of
1:32 or higher (presumed to include most of
those naturally immune).
RESULTS
Although this study was in no sense a safety
trial, it may be said at the outset that no significant
illnesses possibly attributable to the vaccine
virus were observed. The basic data relate
to extent of infection with the vaccine strain, the
¡ Homes without children
cEE Homes with children not in study
~ Homes fed voccine
I Homes fed plocebo
ORAL POLIO VACCINE STUDY
Morgan City Community
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FIG. 1. Map of Morgan City Community showing location of all dwellings and indicating
the participating vaccine and placebo-fed households.
r]] Homes without children
[i Homes with children not in study
Homes fed vrccine
Hormes fed placebo
..., ORAL POLIO VACCINE STUDY
c::a Franklin Community
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FIG. 2. Map of Franklin Community showing location of all dwellings and indicating
the participating vaccine and placebo-fed households.