LIVE POLIO IRUS VACCINES

594 Discussion
594 Disenísion ~ ~ ~ ~ _
that is, initiating immunization with inactivated
vaccine, following up with the administration of
Type 1 live virus vaccine.
For the time being, we are not very worried
about Type 2 and Type 3, although, of course,
we may find that we shall have to add one or both
of those types to our arsenal.
We shall probably start vaccinations at the age
of three to six months, giving combined triple
vaccine plus polio, and then wait until the children
have reached the age of two to three years
before giving the first dose of live virus.
In doing so we feel that the spread of virus
will be better controlled than if we fed infants as,
according to our experience, the rate of spread
from children above the age of two years is
greatly reduced.
However, in our preliminary experiments we
have found that full resistance to re-inoculation
is not established after a single exposure to live
attenuated virus and further, that the titers obtained
are not stable but tend to fall off with
time. Therefore, we intend to add a second inoculation
with live virus during the first year of
school.
There seem to be certain advantages to such a
procedure; it ought to be safe. We are not using
live virus except under the cover of a basic
serologic immunity produced by inactivated virus,
and we may even get around the difficult problem
of extraneous simian viruses in the vaccine in
this way, because supposedly the inactivated virus
vaccines we have been using in the past and are
going to use in the future contain an array of
simian viruses, and probably produce serological
immunity to those agents.
I should like to point out that this program
does not offer any particular organizational difficulties,
at least in our country. Practically 100
per cent of the children born in Sweden remain
under the supervision and control of the children's
health centers up to an age of three to
four years. And, as Dr. Sabin just pointed out,
vaccination with live virus in the schools is easily
accomplished.
DR. BODIAN: I should like to ask Dr. Sabin a
question. What criteria would be used in Cincinnati
to decide that the chain of transmission
has been broken by this program?
DR. SABIN: The criteria would be the incidence
of poliomyelitis virus that would be found in the
population several months after the completion of
the vaccination program and also subsequently.
I believe that all mass vaccination programs
with live virus vaccine which are to be started
from now on, should have not only good clinical
surveillance, but also repeated tests for the
viruses in the community. This ultimately should
indicate the regimen of live virus vaccination that
will be needed to bring intestinal resistance in
the population to a level where one really cannot
detect polioviruses in the community after the
initial period of dissemination.
I do not know what that regimen will be,
whether or not it will require refeeding or how
many times. But this is a beginning, this is a
rational beginning, and I think that virologic
surveillance will indicate what should be done in
the future. The objective is to have a community
without polioviruses circulating in it.
DR. BODIAN: Should no Type 1 viruses be found
later in the summer, having been present in the
spring, will it be assumed that the chain of transmission
has been broken by the feedings of the
a-t^nuated virus to the population in Cincinnati?
DR. SABIN: It is not only that Type 1 viruses
were present in the spring before we started feeding,
but in this population, with 175,000 having
received Type 1 vaccine strains, we actually have
put in a mass of Type 1 virus.
Now, I should say that if we find a great deal
of Type 1 virus we would have very good evidence
that this chain of transmission was not broken.
If, on the other hand, we find none, we can at
least say we found none after feeding 175,000
children with Type 1 virus. If we find a little-I
hope you will give me time to think things over.
DR. BODIAN: I have one more question. First,
I should like to say that I am very appreciative
of what a study like this means, and I think that
there is nobody else more competent than Dr.
Sabin to get at this very difficult problem, because
the type of laboratory surveillance that we
are talking about represents quite a feat, which
Dr. Sabin is fully capable of accomplishing.