LIVE POLIO IRUS VACCINES

DISCUSSION
CHAIRMAN STUART-HARRIS: We shall reconvene
this afternoon first with a discussion on Dr.
Smorodintsev's paper.
DR. KITAOKA: I should like to ask Dr. Smorodintsev
how the live vaccine which was used in
his country was prepared. I should also like to
address the same question to Dr. Gear, in connection
with the preparation of the live vaccine
in his laboratory.
I myself have not yet dared to prepare the
vaccine in my laboratory, until some procedure
is developed to eliminate the possibility of
reversion due to mutation in culture media used
for vaccine production, as mentioned by Dr.
Dulbecco this morning. The seed stock supplied
by Dr. Sabin and Dr. Koprowski is very safe
and avirulent, but during the preparation of the
vaccine there is still a possibility for a mutant
to come out.
DR. SMORODINTSEV: The live vaccine was prepared
in the Leningrad Institute of Experimental
Medicine in accordance with the standards established
by Dr. Sabin. These lots were used in all
field trials and consisted of one batch totalling
approximately 20 liters of each type. This
vaccine was not only tested in Leningrad but in
Sabin's laboratories with results comparable to
the standards set for this type of vaccine. Our
lots represented the second passage of the original
vaccine made in the United States.
DR. GEAR: In reply to Dr. Kitaoka's question,
our vaccine was prepared from Sabin's strains.
The preparation was made from single monkeykidney
lots. The neurovirulence of the original
vaccine sent to us by Dr. Sabin was tested intracerebrally
and also intraspinally, as were also
the derived lots. We derive one lot, which we
set aside as a seed lot, and from that we make
the production lots for issue.
The lot I was discussing this morning has
been tested on 120 monkeys, 60 intracerebrally
and 60 intraspinally, and in no instance in the
intracerebral inoculation was there any sign of
paralysis, The intraspinal inoculation gives
505
somewhat wider lesions than Dr. Sabin has described
in connection with his monkeys, but this
undoubtedly is due to the method of inoculation.
As far as neurovirulence goes, we are satisfied
that it has not gained as a result of passage.
We also tested the vaccine in baby mice, in
guinea pigs, in rabbits, as well as in monkeys,
in tissue culture of non-primate tissues, and in
tissue culture of primate tissues, after the virus
had been neutralized to ascertain that there was
no other virus present in the vaccine.
DR. BODIAN: Prof. Smorodintsev's study is so
impressive that I am sorry we have so little time
to discuss it. I have been impressed by the fact
that there was an attempt to set up some type
of control groups. I think the advantages of this
are, or should be, obvious.
Prof. Smorodintsev did mention two things
that seemed to me to be somewhat contradictory,
and I would very much appreciate an explanation
or an interpretation of this. First of all, it
was emphasized that the expectation of what
was referred to as "blind immunization," that is,
by secondary spread, was very low. Yet I
thought I heard a statement that in the control
groups there was evidence of diminishing polio
rates, parallel with the decline in the vaccinated
group. I also thought I detected, at least in some
of the areas, that the external control group
showed a decline of incidence parallel with the
decline in the vaccinated group. I realize that
there may be several factors going along together
here.
Finally, I wish to congratulate Prof. Smorodintsev,
among other things, on having cleared
up, in my opinion, some of the problems of
scheduling, because it does appear that he has
very convincingly demonstrated the virtues of
repeated immunization.
DR. SMORODINTSEV: The total decline of polio
cases in the whole vaccinated group depended
on the extent of immunization, which included
not less than 65 per cent of the population.
Under these conditions we removed the most
significant portion of cases expected aud ex-