LIVE POLIO IRUS VACCINES

Capacity of Live Attenuated Polioviruses to Cause Human Infection 181
as the response to Type 1 attenuated poliovirus
was concerned, an interfering role on the part of
non-poliovirus enteroviruses was appreciable. If
any particular enterovirus could be incriminated,
it may have been ECHO 12. With Type 3, however,
there was no evidence of interference. Actually,
the opposite may have occurred (see Fig.
10).
Figure 10 shows the rates at which potential
vaccinees excreted Type 1 poliovirus as compared
with rates at which members of the same group
were excreting non-poliovirus enteroviruses.
Prior to the administration of the triple vaccine
and two months later, the incidence of non-polioviruses
was about 20 per cent, but during the
period of greatest infection with polioviruses this
level was reduced to about 10 per cent.
Thus, the impression we have derived from this
study is that, if any virus can be regarded as an
"interfering agent," it was the Type 3 attenuated
poliovirus used in the vaccine. This "took" so
well and was so efficient in producing lasting infection
that it dominated the scene and appeared
to crowd out the other competing attenuated
polioviruses, and perhaps, the "competing" nonpoliovirus
enteroviruses as well. The ultimate
extent to which this dominant effect of Type 3
poliovirus actually excluded or merely postponed
ultimate infection in the vaccinees by the two
other attenuated polioviruses is not known, for
our observations on antibody determinations cover
only 11 weeks in these index children.
Spread within Households. The findings on
intra-familial spread reflect fairly closely the infectivity
rates which resulted from feeding these
three attenuated strains to the index children in
the form of a trivalent vaccine given on two occasions
a month apart. The strain which "took"
the best spread the best. Infectivity and spreading
capacity seem to be closely related properties.
I cannot say that they are identical. Thus, during
the ll-week-period of observation, Type 3
poliovirus, given at a dose of 105 ' 5, which had the
capacity to infect at a rate of about 91 per cent
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