LIVE POLIO IRUS VACCINES

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TOPIC II. SAFETY. (B) FIELD EVIDENCE OF
SAFETY
(continuation)
15. FIELD AND LABORATORY EXPERIENCES WITH
THE CHAT STRAIN TYPE 1 POLIOVIRUS*
SVEN GARD
The Department of Virus Research, Karolinska Institutet Medical School, and the
State Bacteriological Laboratory, Stockholm, Sweden
DR. GARD: At the First International Conference
on Live Poliovirus Vaccines a brief report 1
on a Swedish small-scale field trial with the
CHAT strain Type 1 virus was presented. This
trial was initiated in November 1957 with participation
of 20 volunteer families. A second test
vaccination of 107 families was performed in the
winter of 1958-59. In 1959-60, finally, three separate
controlled studies have been conducted and,
in addition, less rigidly controlled group vaccinations
have been carried out. A total of about
1.000 persons have now been vaccinated.
A detailed report of our various findings will
be presented elsewhere. I should mention, however,
or point out, that we have applied live virus
only under cover of a previous basic serologic
immunity produced by administration of inactivated
vaccine. A dose of 106 TCID 50 was used
throughout. In 275 persons without pre-existing
natural immunity this dose never failed to produce
infection. It should be pointed out, however,
that in more than 2500 stool specimens from
about 750 persons participating in the various
projects non-polio viruses were encountered on
two occasions only, one enterovirus and one adenovirus.
Apparently, therefore, the experiments
were conducted in the absence of interference.
All feedings were done in the period January
through April.
* This work was supported by grants from the
Swedish Society against Poliomyelitis.
187
In the present connection, I will touch on two
aspects of the use of live virus vaccine. The first
concerns spread of virus to contacts.
Spread of virus to contacts. It was previously
reported 1 that, in the first trial, a spread of virus
to susceptible family contacts occurred mainly
from vaccinees less than two years old. Of 12
children below the age of two years, seven were
spreaders as against none of seven children above
that age.
In the subsequent trial all index children were
four years old; of 63 children with susceptible
family contacts only three became spreaders.
In 1960 two separate studies of this question
were conducted. In one trial2 two comparable
groups were included. Among 32 families with
index children less than two years old spread of
virus occurred on 13 occasions, whereas only one
instance of contact infection was observed in 30
families with index children above the age of two
years. The results summarized in Table 1 indicate
that the young children cause contact infections
more than 10 times as often as the older
ones.
A similar study 3 was set up in an institutional
school for blind children with a total of 152 inmates,
aged seven to 19 years. Dormitories for
girls and boys were located in separate wings or
buildings; play rooms and dining rooms were
shared; teaching was coeducational in nine
grades and 14 separate classes according to age.