LIVE POLIO IRUS VACCINES

Spread of Vaccine Strain of Poliovirus in Southern Louisiana Communities 145
Our own exploration of interhousehold spread
began in relation to the previous household
studies when we demonstrated spread following
deliberately arranged, brief play exposure of
children. This led us to the study herein reported
which was designed specifically to explore
the dissemination of vaccine virus under optimal
conditions in the unmanipulated community. Although
preliminary results have been reported
elsewhere,`0
substantial additional information is
now available.
METHODS AND MATERIALS
General plan of the study. Several small, welldefined,
lower economic neighborhood communities
in the Evangeline area were chosen as candidates
for study on the basis of our knowledge of
their physical and social characteristics and our
estimates as to probable sero-immunity patterns
as derived from previous investigations. 4 -6 Within
each community approximately 25 households
were recruited on a voluntary basis, and from
these were obtained pertinent data, including a
Salk vaccination history (later confirmed through
official health records), and blood specimens from
each member. Review of the vaccination history
and the results of testing the sera for neutralizing
antibody permitted us to select two communities
containing a high proportion of children susceptible
to Type 3 poliovirus.
Within the chosen communities the participating
families were paired, one to receive vaccine
and the other an identical appearing placebo,
only on the basis of the number of probably susceptible
children under 15 years of age and
address to insure that the vaccinated families
were widely scattered. Feeding was begun early
in June, just after school was dismissed. All
children in a household received the same material,
vaccine or placebo, the specific nature of
which was not divulged until the end of the observation
period.
Base-line blood and stool specimens were obtained
from each child on or just before the day
of feeding. During the next 12 weeks, with occasional
exceptions, additional fecal specimens were
contributed twice weekly. These were collected
during weekly visits made by the nurse epidemiologist
(D.R.L.) to obtain information as to illness
and significant social activities of the children.
At the end of August, terminal bloods were
collected and, as a promised reward, all children
were fed trivalent vaccine.
Vaccine strains and administration. Because
of the susceptibility status of the chosen communities,
only the Type 3 (Leon 12a 1 b) strain
was used. This was provided by Dr. Sabin from
the large pool that had fulfilled his rigid criteria
for purity and attenuation. 1 ' The stock vaccine
was distributed in amounts appropriate to the
needs of the individual families, the family-identified
containers then being held at -20 C. until
just before use. Disposable medicine droppers
were employed to squirt 1 ml. amounts (containing
7.3 logs of virus) into the oral pharynx of
each child. Placebo salt solution with phenol
red was packaged and handled in the same
manner.
Laboratory procedures. The laboratory methods
employed were standard and have been described
in detail elsewhere.' 12 Monolayer cultures of
monkey-kidney cells were employed throughout
and visual detection of cytopathic effect was used
as the index for virus isolation and identification
and for serum neutralization. Serum antibody
titers are expressed as 50 per cent end-point
values in terms of the final dilution of serum and
were based on the use of two cultures per twofold
serum dilution mixed with aliquots of virus
calculated to contain approximately 100 TCID50
per culture inoculum.
Characteristics of the study communities. The
two communities chosen were small, distinct
neighborhoods located in the town of Morgan
City and Franklin, Louisiana. Their physical extent
and the distribution of the study households
are shown in Figures 1 and 2. Although not isolated
from their respective towns, each constituted
a relatively homogeneous play community.
Special features propitious to virus spread include
low economic level and associated poor environmental
sanitation with many functioning
outdoor privies, poor personal hygiene as indicated
by the usual unwashed state of the children,
large families and intense social intermingling.
The pertinent population data are presented in
Table 1, which indicates, in particular, the relative
overall abundance of the children and the
sizeable proportions of the child population seeded
by vaccine feeding (17 per cent in Morgan
City and 43 per cent in Franklin) or designated