LIVE POLIO IRUS VACCINES

Use of Attenuated Live Poliovirus Vaccine in Cuban Children
367
recreation camp. Blood samples were collected
at the time of vaccination and again seven weeks
after vaccination.
The pre- and post-vaccination type-specific
seronegatives found in these 167 children are
tabulated in Table 3. The seronegative to positive
conversion rate for all three poliovirus types
was 76 per cent. It thus appears that under our
test conditions, the trivalent fluid vaccine was
associated with conversion rates which are comparable
to those obtained with the monovalent
capsule feedings at both the seven- and 15-day
intervals.
COMMENT
Of the 496 children included in the monovalent
and trivalent vaccine trials described above only
92 were without antibody for one or more types
of poliovirus at the time of vaccination. Collectively
these 92 children represented a total of
109 type-specific seronegatives, which is indicative
of a relatively high rate of natural immunization
among the Cuban children under observation.
Seronegative conversion rates calculated
from data obtained in such a population are
liable to considerable variation unless much
larger numbers of children are studied than were
involved in the present trials. A criterion which
is more comprehensive and informative than
either conversion rates or geometric mean titers
for expressing poliovirus immunity has been suggested
and is described in the appendix. This is
the seronegative index which is intended to express
the relative hazard of paralytic poliomyelitis
in an adequately sampled community. It
assumes that the number of seronegatives in the
study population is indicative of the chances of
paralytic disease when virulent strains of virus
are introduced. The maximum hazard would be
100 per cent in a population of triple-negatives.
Natural infections reduce this maximum hazard
progressively so that the ratio of seronegatives to
seropositives at any given time is a measure of the
poliomyelitis potential. In Table 4 the seronegative
indices before and after vaccination are presented
for several of the Cuban oral poliovirus
vaccination trials.
Here it may be seen that in spite of varying
type-specific and total seronegative conversion
rates, the net residual poliomyelitis potential in
these vaccinated children has been reduced to the
low level of an adult population in which paralytic
poliomyelitis is most infrequent.
CLINICAL OBSERVATIONS
As we have reported in connection with the
trials described earlier, there have been no instances
of illness that can be attributed to the
vaccine among children who have been fed the
attenuated strains of poliovirus in the present
trials. There are, however, several observations
regarding pre-existing and concurrent conditions
that are of interest in relation to the administration
of oral poliovirus vaccine.
TABLE 4.
SERONEGATIVE INDICES IN
VARIOUS POLIOVIRUS VACCINATION
TRIALS IN CUBA
TRIAL TYPE R-DIIi
IOMtlR TYP 81SPlC UIC 8MOM.TIVE
GROUPS VACC I51 I NTERVAL (RI L1!7. S1OBR DI-e_
PIE POST PIE POST
7,8 mIONO 7 183 41 13 7.46 2.36
3,5,6* " 7 361 76 8 7.02 0.C0
11 " 15 146 2 7 5.9 1.6
4* " 21-35 105 15 5 4.7 1.6
2* 0 62 36 4 19.3 2.1
14a-18** TRIVAL. 0 360 91 11 8.4 1.0
14b.22 " 0 167 42 10 8.4 .O0
TOTAL 1384 327 56 7.87 1.34
* Previously reported (3).
* Previously reported (4).