LIVE POLIO IRUS VACCINES

DISCUSSION
CHAIRMAN ZHDANOV: This paper is now open
for discussion.
DR. SABIN: I wonder if Dr. Verlinde would
indicate the number of families in Leiden in
which the vaccine strains were fed. I think his
data are of importance to supplement other available
epidemiological data in which the feeding
was done on a much larger scale. I know that
he fed only a small number of families in the
city of Leiden, and that therefore it represents a
situation in which a small number are fed, and
a larger number are exposed. This supplements
the tests in the Soviet Union last year, where approximately
50 to 60 per cent of the population
were fed in some regions, and also more recent
studies in other areas where 80 to 90 per cent
of susceptible age groups were fed. I wonder if
Dr. Verlinde could, for the record, indicate how
many families were actually involved in the Leiden
feedings over the two-year period.
DR. VERLINDE: Approximately 40 families have
received vaccine strains in the Leiden region.
DR. BODIAN: I should like to ask Dr. Verlinde
whether he has any measure of the spread of
virus from those families into the community, because
we have here a very excellent situation for
assessing the epidemiological significance, if any,
of an increase in neurovirulence. Just as we have
data from Professor Smorodintsev's study in regions
where there were large numbers of unvaccinated
individuals, here we have even a larger
group of contacts who may have been exposed to
excreted virus. Is there any measure of the
spread of the strains?
DR. VERLINDE: Unfortunately we do not have
that measure. It appeared to be very difficult to
obtain fecal specimens, for instance, from the
neighbors of the families, and especially from the
school children with whom the vaccinated children
had been in contact.
The only measure we have is the virological
examination of stools from children who exhibited
some kind of illness during the three years.
But in the normal population we have, unfortunately,
no evidence of spread of the vaccine
virus as could have been determined by examination
of a large number of stools from healthy
contacts.
DR. MELNICK: We are going to hear a number
of papers about vaccine effectiveness as the Conference
proceeds. In this regard it is of interest
to call attention to the record of poliomyelitis
that Dr. Verlinde showed us for The Netherlands.
If we look at Table 1 of his report,* we find
that the number of polio cases reported for 1956
to 1959 varied from over 2,000 in 1956, to 216
in 1957, then fell sharply to 37 in 1958, and to
only 12 in 1959.
Had Dr. Verlinde carried out a mass vaccination
trial instead of feeding virus to a few
families, we would have here an excellent example
of what might well have been considered
to be vaccine effectiveness.
DR. VERLINDE: Salk vaccination started in The
Netherlands in 1957, and in the subsequent years
an increasing number of children has been vaccinated.
I do not know exactly up to what age, but
I think up to 9 or 10 years. This year children
up to 14 or 15 years of age will be vaccinated.
During the first two years, 1957 and 1958, only
children of one and two, perhaps three, years
of age have been vaccinated.
CHAIRMAN ZHDANOV: If there are no further
comments, we shall proceed with the next paper
on the "Spread of a Vaccine Strain of Poliovirus
in Southern Louisiana Communities." The presentation
will be made by Dr. Gelfand.
* See p. 134.
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