LIVE POLIO IRUS VACCINES

iiiii iirrrimrmiriiiilllniririiiiiiiiirmiiinn
iirmiiiiii irmnrmiirmiiiiii iiirmniiiiiUUIiiiiiiiiiiiiiiiiiiiiiiiiiii
SUMMARY OF THE CONFERENCE
CHAIRMAN VARGAs-MÉNDEz: I should now like
to call on Dr. Payne to read the summary report
of the Conference, prepared by the Summary
Committee.
DR. A. M. M.-PAYNE (Chief Medical Officer,
Virus Diseases, World Health Organization):
As last year, the document before you was
prepared by an anonymous group which has attempted
to summarize the opinions of all participants
at the Conference and to give an
objective reflection of the different views expressed
here. No attempt has been made to draw
conclusions, or to make recommendations, since
that was not the purpose of this Conference,
which was essentially to bring all available data
into the open, onto the table, and to elicit the
differences of opinion which may exist, in the
hope of eventual resolution by further work.
After Dr. Payne read the document, it was
reviewed and discussed by the participants and
the following text was unanimously approved:
Introduction
In the year which has elapsed since the First
Conference on Live Poliovirus Vaccines, intensive
studies of the properties and value of these vaccines
have been continued or undertaken in many
countries of the world.
These studies have included detailed investigation
of the characteristics of vaccine virus
strains before and after multiplication in man
and of wild strains, and of means of differentiating
them. Extensive investigations of the effects
of the administration of the vaccines to individuals,
in families, in institutions, and to particular
groups, have also been carried out. They
have also been used on an increasingly large and
even massive scale under a great variety of geographical
and climatic conditions. Much new
factual information on their use and in particular
on their safety and efficacy has been accumulated.
This Conference has provided an opportunity
to review this work. Some of the problems have
600
been more clearly defined and some of the questions
answered.
Laboratory Evidence of Attenuation and Safety
Additional evidence has become available concerning
the comparative properties of the proposed
vaccine strains. The findings regarding
neurovirulence for monkeys reported last year
have been confirmed and extended although their
epidemiological significance remains to be established.
In addition, some of the strains have
been shown to have neurovirulence for monkeys
when injected intramuscularly. A considerable
amount of information was presented concerning
markers and their possible correlation with
virulence. These results were disappointing as
they failed to show, in the case of any one marker
by itself, satisfactory correlation with neurovirulence.
This avenue of endeavor still appears
fruitful and evidence concerning some promising
new markers was presented. A number of reports
confirmed the instability of many of these
strains after passage through the human intestinal
tract, as determined by markers and changes
in monkey neurovirulence. In some instances
these changes were demonstrable after tissueculture
passage alone. This instability limited
the use of such markers in the positive identification
of vaccine strains after multiplication in
the human alimentary tract and their differentiation
from wild viruses.
A limited amount of information was available
concerning viremia in man following the administration
of live vaccines. One report indicated
that this was not infrequent in the case of one
set of strains, while another report which concerned
a single type of a second set was negative.
This whole problem requires further investigation
and standardization of methods.
Many data were available in reports on a
variety of subjects concerning laboratory properties
of these strains. This information will be
useful in the development of the ultimate control
criteria for live poliovirus vaccines. One item
of special interest was the denmonstration of the