LIVE POLIO IRUS VACCINES

596 Discussion
596 Díscussion~~~~~~~~~~~~~~~~~~~~~~~
more effective in eliminating paralytic poliomyelitis.
I think at this meeting we have got rid of a
great deal of loose talk about single doses of live
virus vaccine producing long-lasting immunity.
and about epidemics of immunity. Now we hear
of multiple doses and we are not quite so certain
about the duration of immunity.
I think we must not be motivated by theories
of obsolescence, but obviously, as we all are, by
what is best.
One thing which I believe is also very clear to
most of us is that we have to give very careful
consideration as to which of the six strains of
live virus vaccines should be used in further
studies.
DR. SMADEL: I believe this has been a most interesting
and productive colloquy between Dr.
Bodian and Dr. Sabin.
My comment is one regarding certain of the
legal requirements for licensing, which I am sure
have not been made quite clear to many of the
people here, certainly not from the scientific discussion
that went on between the two.
The Surgeon General of the United States is
not empowered to issue a license for any biological
until a manufacturer has demonstrated his
capacity to produce in a consistent manner a
product which is potent, safe, and useful. Thus,
licensing is essentially the final act in the research
development of a new biological and is accomplished
just before the material is ready for general
use and for distribution across state borders.
This procedure of licensing is different from
those under which our colleagues in England,
Russia, and other countries operate.
DR. KITAOKA: During the Conference many results
were published on field trials of the three
kinds of vaccines which are called by the same
name of "live poliovirus vaccine." Each was prepared
by using different strains developed by Dr.
Sabin, Dr. Cox, and Dr. Koprowski, respectively.
I shoud like, frankly, to ask whether one of them
is safer than the other two and if the difference is
clear enough to prefer it for use in the community.
Also, which of the attenuated poliovirus
strains used for the vaccines might still be neurovirulent
to some extent, according to the observations
made during the mass vaccination trials.
We had an experience with no untoward reaction
following monovalent vaccine but not with trivalent.
DR. GARD: In reply to Dr. Sabin, I shall only
say that we have not disregarded Types 2 and 3.
The reason why we are concentrating on Type 1
live virus is that we consider the protection obtained
with the use of killed virus vaccine against
Types 2 and 3 as being adequate and of longer
duration, according to our tests, than against
Type 1. That is the reason why we intend to supplement
the killed virus vaccine with Type 1 live
virus vaccine only.
The future may show that we have to include
another type. But for the time being we are only
worried about Type 1.
DR. SABIN: Dr. Kitaoka has again raised the
question of the use of trivalent and monovalent
vaccines, and I should like to take this opportunity
to indicate what my own guiding principles
are.
Under conditions in which little interference
from other viruses may be expected, such as we
have shown to obtain in Cincinnati, even among
slum populations during the spring of the yearand
maybe even less during the winter months-I
believe that the feeding of the individual types
not only provides the best incidence of immunity
for each individual type, but, having the maximum
opportunity for extensive multiplication in
the intestinal tract, does, on the basis of already
existing data, give us the best hope of obtaining
the maximum resistance of the intestinal tract.
On the other hand, in other parts of the world
where we know that there is massive infection
with other enteric viruses throughout the year,
and where we know there is such extensive dissemination
of naturally occurring polioviruses
that children become naturally immune to all
three types by the time they are four or five years
old, under such conditions we have evidence that
nature itself can greatly help in the dissemination
of the vaccine viruses.
Under such conditions 1 believe that the experiment
that I reported in Toluca provides an
indication of how, by two feedings of trivalent
vaccine, one may obtain not only a very high inci-