LIVE POLIO IRUS VACCINES

564
Efficacy-Field Evidence
and by age is shown in Fig. 1 and Tables 2 and 3.
Fig. 1 gives the calculated percentage of children
reached by the program, by province. In certain
places the percentage may seem low, and transportation
facilities and other factors influence the
number of children vaccinated. Table 3 summarizes
the results of a prevaccination serologic survey
in children under 11 years of age, whose ac-
celerating rate of infection in relation to age is
strikingly illustrated in Figure 2. Table 3 also
shows how the percentage of seronegatives by type
diminished rapidly as age increased. In Table 4,
the number of serologically susceptible children
who received the vaccine is estimated by applying
the percentage of type-specific seronegatives
.%-100
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AGE
FIc. 2. Type specific seronegatives by age-prevaccination survey of 794 sera in Costa Rica.