LIVE POLIO IRUS VACCINES

Susceptibility of Newborn Infants to Infection with Poliovirus Strains 311
added recently to comprise babies receiving vaccine
in 1:1000 dilution. None of these has yet
received the vaccine. This table also shows the
number of babies vaccinated to date in each subgroup
and the numbers demonstrated to have become
infected or to have failed to become infected
as indicated by the presence or absence of
homologous virus in the sixth-day or later specimen.
Considering first the monovalent feedings
in very young infants (groups 1-3), and realizing
TABLE 2.
PRELIMINARY RESULTS OF ORAL VAC-
CINATION BASED ON FECAL EXCRETION OF VIRUS
OF HOMOLOGOUS TYPE
-nrror n bates Pregsoe of helogne
¥Tra rim lin 6-da s ldeen
Subgrup ldifited vaecine
n=ber(l) (e)goal to date Yes no lcplete tudy
0 lo 9 o 1
b e 10 D
o10 12
11 10
0
9
0
h U
3
3,
d 10 0
2a 6 6 6 0 0
b 10 10 7 1 2
c 10 10 7 0 3
d 10 0
3. 10 10 9 1 0
b
c
15
15
10
10o 6
3
2 2
d 10 0
h o 2 1 1 0
5 10D 1 a 1 1
1in 6 6 0 0
e 10 6 6 o 0
6. 20 1 9 1 5
b 10 10 10 0 0
7 15 1U' 0 8 3
Total 201 lh9 102 22 25
IX) See Table 1 for description of subgroups.
* Recruited but not vaccinated.
the small numbers available in each subgroup,
the Type 2 component of the vaccine seems to be
the most highly infectious, followed by Types 1
and 3 in that order. A single failure was found
with Type 2 in 1:10 dilution, but none with the
1:100. The 50 per cent end-point of infectivity
with Type 1 vaccine may be at about the 1:100
dilution since only four of eight babies became
infected. The results following Type 3 administration
are most scattered, some failures being
recorded throughout the range of dilutions used.
Since a single dose of undiluted Type 1 vaccine
virus appeared to result in infection, it was
decided to discontinue the recruitment of babies
for group 4, those who were to be fed this material
on three successive days. Only two infants
were fed on this regime, and it was very surprising
to note that one failed to excrete virus on the
sixth day after the first dose. Serologic study
later may reveal that infection had occurred
nonetheless.
The babies approximately 30 days old (group
5) who have so far been fed have become infected
with the sole exception of one child who received
undiluted vaccine. The latter unquestionably received
the full dose without wastage, and almost
certainly failed to be infected since fecal specimens
collected every second day were consistently
virus-free. Whether this group as a whole demonstrates
the greater susceptibility of month-old
babies over newborns is difficult to decide from
the small numbers involved.
The duration of fecal excretion, and the consistency
with which virus may be isolated from
serial specimen collections is illustrated in Table
3. Note that the choice of the sixth day was a
fortunate one for the collection of a single specimen
from the majority of children, since from
only one of these babies who were at some time
shown to have become infected was a negative
specimen obtained on the sixth day. However,
note also that no single specimen can guarantee
to demonstrate the infection of every infected
TABLE 3.
DURATION AND CONSISTENCY OF FECAL
EXCRETION OF HOMOLOGOUS VIRUS FOLLOWING
ORAL ADMINISTRATION OF UNDILUTED VACCINE
TO FIRST 24 BABIES OBSERVED IN LONGITUDINAL
FASHION
Vaccine Presence or absence - of lrs in speíie n
Subgroup rim ollected ci on indicated da, aftcr ccinstion
nuber (r) type 0 2 h 6 -28 lh 1 21
la 1 - + _ -
7; 2 _oNC f + + · _ _
2a 3 _ C ' .+ .-
5. -
So. + . _-
(X) See Table 1 for description of subgroups.
·Not collected.