LIVE POLIO IRUS VACCINES

DISCUSSION
CHAIRMAN ZHDANOV: Thank you, Dr. Horstmann.
This paper is now open for discussion.
DR. GEAR: I should like to ask Dr. Horstmann
if she considers that her results are a recommendation
for feeding trivalent vaccine, rather
than monovalent vaccine? Feeding trivalent
vaccine more than once gives an opportunity for
the intestinal tract to become infected with the
particular type for which antibodies are not
present, and 1 would be grateful to have Dr.
Horstmann tell us whether she thinks that her
results are in favor of feeding triple vaccines,
rather than monovalent vaccine.
DR. HORSTMANN: I think the results have to
be interpreted in relation to the environment,
the age, and immune status of those to be vaccinated.
On the basis of our findings, I would
not recommend trivalent vaccine if one expects
to accomplish rapid immunization of a triplenegative
child with one dose of vaccine. Perhaps
when we know more about optimum dosage level
combinations for any particular preparation a
single dose of trivalent vaccine will be more
effective than is currently the case.
In the meantime, my feeling is that if one
wishes to use the trivalent vaccine, it should be
given repeatedly, and at somewhat longer intervals
than we used.
DR. Cox: These results confirmed what we
found out about our Type 2 strain. The Type 2
strain of course has been the most modified by
laboratory manipulations of any of the strains
we have. Actually, our Type 3 strain is the only
one of our strains that has never been adapted to
a foreign host. We think this may be partially
responsible for its greater ability to infect the
human gut.
Furthermore, this particular batch of vaccine
was made up in a considerable hurry and did
not contain as much virus as we had intended.
Data to be presented later will show results
obtained with a vaccine containing more virus,
namely, 6.1 logs of virus per strain. Actually,
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in the Florida trials, where we apparently obtained
our best results, we compensated somewhat
for the Type 2 deficiency by actually putting
in a bit more than 6.1 logs per dose.
We have found, by asking people who have
worked with monovalent versus trivalent, that it
is much better to feed trivalent twice, and certainly
at a longer interval than one month, than
to carry out monovalent feedings.
We believe that there is still resistance in the
gut which may interfere with feeding trivalent
vaccine at a one-month interval. But when it
comes to practicality and expense, it is much
easier to feed trivalent twice than it is to feed
the monovalents separately.
We have been considerably encouraged by
what we have seen with the trivalent vaccine
because I think the results Dr. Horstmann obtained
are probably the poorest we have seen and
certainly somewhat inferior to our other data.
This may be due to the quantity of virus fed, and
perhaps to some other factors we do not understand
as yet. To be sure, they are sufficiently
encouraging so that we feel it worthwhile to go
ahead and solve this problem. There is no doubt
in our minds that this can be done.
DR. FLIPSE: I should like to ask Dr. Horstmann
if she has, and if so could make available for
comparison, the conversion data at the 1:4 level.
There is considerable disagreement, obviously,
as to its significance, but it would make it possible
for those of us who are reporting data in
terms of both 1:4 and 1:16 conversions to compare
her data with other data.
DR. HORSTMANN: As I indicated in our study,
all of the homotypic negative children who became
infected and converted, with one or two
possible exceptions, developed antibody titers
considerably greater than 1:16. Therefore, the
conversion rates at 1:4 are virtually the same as
at 1:16. Furthermore, we used the CPE tube
neutralization method in testing the sera. This
method measures high avidity antibody and gives
lower titers than the pH colorimetric test which