LIVE POLIO IRUS VACCINES

Capacity of Live Attenuated Polioviruses to Cause Human Infection
183
TYPE
I
NO. INDEX CHILDREN SPREADING * I1
NO. SIBLINGS INFECTED - 24
UD
II
0lo
9
8
7
6
5
4
3
2
P.
J
m
7n
U-
o
o
2 lo
9
8
TYPE Im
7T
11
[ir]
PI·;l 1·1_I ·_··1 E: r_· r:·__··l I·__···_·II I··I·I
E
····I
E ur····l
....
lFi1 1
NO. INDEX CHILDREN SPREADING =28
NO. SIBLINGS INFECTED = 36
6
5
4
3
(-7) (-5) (-3) (-1) 0 I 3 5 7 9 11 13 15 17 19 21 23 25
FIC. 13. Days of onset of the siblings' infection as related to the index child's infection with Type 1
and also with Type 3.
Almost 20 years ago, I made the mistake of saying
that the situation with regard to family epidemics
would "seem to indicate that most families
become infected through a common source
. . Our present data would belie this explanation
and point rather to the fact that the
attenuated viruses used in this trial spread so
quickly from the index child in the family that
it may well be that within 12 to 18 hours after the
ingestion of attenuated polioviruses an index
child might be considered as capable of infecting
his intimate playmates. This eliminates the
necessity of assuming that an almost simultaneous
infection in several members of a family necessarily
means an extra-familial common source
of virus.
COMMENT
This report on the experimental epidemiology
of poliomyelitis, based on a short but rather intimate
study of a trivalent, oral poliovirus vaccine
trial administered twice and under rather special
host and environmental circumstances, has
brought out some of the complexities of achieving
an optimum rate of 100 per cent "takes" by the
current procedures used. However, there is no
intimation presented here to suggest that this
goal cannot be achieved. The report has pointed
out a considerable difference in the capacities of
these three particular attenuated poliovirus
strains to "take," even though all were given in
presumably the same dosages, namely about 106 ¥ .
The rate of "takes," as measured by antibody
conversion rates, was more than 90 per cent with
Type 3, about 75 per cent with Type 1, and much
lower for Type 2. This differential capacity to
infect the index children was mirrored by a
parallel capacity for these viruses to spread to
siblings. Indeed, the ease and the speed of intrafamilial
spread on the part of these attenuated
polioviruses was striking.
Finally it should be emphasized that the results
of this trial, utilizing as it did a rather
special and unofficial method of giving the vac-