LIVE POLIO IRUS VACCINES

transplacental antibodies, or antibodies of any
type, are present in the pharynx to a much
greater degree than in the intestinal tract.
In our own premature study, the virus was
given by gavage directly into the stomach. With
full-term infants, the virus was given in a volume
of milk, so that most of it passed down the
esophagus and past the pharynx.
If I interpret Dr. Robbins' statements correctly,
1 cc. of the virus was delivered by
dropper into the pharynx; in Dr. Krugman's
study, a similar procedure was followed, I take it.
Could it be, then, that some of the influence of
transplacental antibody shown in the results may
reflect the implantation of the virus in the
pharynx, whereas the relative lack of effect on
infection that we have found, may reflect the
administration of the virus as directly as possible
into the intestinal tract?
Second, I have been interested-from a biological
point of view-in the half-life of transplacental
antibody, apart from the necessity of
knowing this value for the evaluation of antibody
responses of infants, and I took the liberty of
calculating Dr. Krugman's data which he so
kindly has given us. By my rapid computation,
the geometric mean half-life of those data here
would be something less than four weeks. Therefore,
I think, as I am sure he realizes, that he
has been perhaps too conservative in his criterion
of antibody response of infants. If he had
used a lower figure for the half-life, then more of
the infants would have shown some apparent
response.
Of course the six-month blood determination is
certainly the most important and the most crucial
in determining the response of these infants.
Before that, it is sometimes hard to try to calculate
what should have happened, but, at six
months it is clear whether the infants have responded
or not.
DR. Cox: There is no doubt that Dr. Gear's
question is very important. The data that we
have are very meager, since they actually consist
of only one case.
It so happens that my own daughter was fed
our polio vaccine within the first two months of
pregnancy. At the time I did not known that she
was pregnant. However, she was fed trivalent
Discussion 327
Discussion 327
vaccine even though she was negative to Types 1
and 3.
All three of our grandsons were fed trivalent
vaccine in the third month of life. All three
strains were found to be excreted in their stools.
This past spring, they were re-fed, and only the
youngest, now 16 months old, excreted virus, and
only Type 2.
Our oldest grandson, who is now five years old,
has been fed vaccine on four consecutive years,
and the past two years he has failed to show excretion
of virus.
These limited data do not mean much perhaps,
but they may give us a general idea as to what
to expect.
While I have the floor, I should like to tell my
friend Dr. Sabin, that I really was not surprised
to see the coming and going of virus strains
being excreted, but I was surprised to see that
Type 2 was being excreted so long, because in
this respect our Type 2 is rather poor compared
to Types 1 and 3.
I do not like to belabor the point, but I should
like to point out that in many ways what we have
done with live poliovirus vaccine has followed the
almost perfect model of Newcastle disease in
poultry. I am not sure that I mentioned this work
this past year, but we had a very serious problem
in trying to immunize newborn chicks against
Newcastle disease. Like everything else in
virology, we have two basic conditions to consider:
quality of the strain and quantity of
material.
We found out quite early that there was no
particular problem in immunizing newborn
chicks, derived from non-immune dams, with
our particular strain of Newcastle, which is the
Blacksburg strain, provided we used an amount
of virus in excess of 4.5 logs. If we went below
4.5 logs, then we obtained very little protection.
We also found that we could immunize baby
chicks derived from non-immune dams with 4.5
logs of virus or better, by any route.
On the other hand, when we came to the problem
of immunizing newborn chicks derived from
immune dams, we found that no matter how
much virus we inoculated by the intramuscular or
subcutaneous routes, we could get no real protection
as determined by subsequent challenge.
However, regardless of whether baby chicks
are derived from non-immune or immune dams,