LIVE POLIO IRUS VACCINES

Spread of Vaccine Strain of Poliovirus in Southern Louisiana Communities 151
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WEEK OF OBSERVATION
FIG. 5. Vaccine virus excretion by week of observation.
munity observation. Since, in at least two studies,
pre-existing infection with such viruses has been
observed to block infection with orally administered
vaccine strains,l3 1 4 one might anticipate
that this abundant occurrence of wild enteroviruses
would provide additional examples of
interference. Although numerous children in
Morgan City and Franklin households were undergoing
infection with P1, B2, or B3 viruses
when they were fed 7.3 logs of P3 vaccine virus,
only two in the low-titer group, both with B2
infections, failed to develop immediate alimentary
infection with P3 virus.
Examination of Tables 4 and 5 provides no
evidence that other enterovirus infection interfered
with spread of the vaccine strain. Not only
did several families escape invasion during the
period of most active vaccine spread despite freedom
from other infection but, in seven instances,
a household was invaded in the same week by
both the vaccine strain and a wild virus. Further,
in Franklin households 227 and 232, the vaccine
strain entered during the first observation week
and displaced a pre-existing infection with B2
virus.
In Table 6 the episodes of wild enterovirus infection
are summarized for the vaccine and
placebo families in each community. Of some
interest is the fact that the viral flora of these
neighboring communities differed significantly.
Coxsackie B3, E14, and E19 were virtually restricted
to Morgan City as were B5 and E7 to
Franklin.
Of perhaps greater interest is an observation
suggesting that administration of the
vaccine virus may have provided brief protection
against infection with wild viruses.
During the
first two weeks after administration of the vaccine,
the vaccine-fed households experienced but
a single wild virus episode, whereas seven were
detected in the placebo-fed families.