LIVE POLIO IRUS VACCINES

Behavior of Cold Mutants of Poliovirus in Human Beings 103
103
out at 360 C. and at 300 C. However, for a ever we switched from one temperature to another,
the virus was adsorbed and the unad-
period of eight days at 250 C., there was no
effect even though the multiplicity of virus to sorbed virus was washed out; only the progeny
cells was almost one thousand.
coming out at the new temperature was used.
At 14 days there was still no complete cytopathogenic
effect. Only a few cells were af-
these consecutive selections we obtained a virus
The main point here is to show that after
fected at the highest multiplicity, with no progression.
but also as extensively at 250 C.
which now still multiplied very well at 360 C.,
Seven passages at 330 C. altered the situation Essentially, Fig. 1 shows what happened with
very slightly, and the results obtained after five the Type 1 strains.
and 10 passages at 300 C. can be seen. There Figure 2 shows that the initial virus had very
was still no complete cytopathogenic effect during
a period of eight days at 250 C., but there gradually it increased. Initially there is a dip
low capacity for multiplying at 250 C., and
was gradually increased activity at this lower in the yield of virus when multiplying at 250
temperature.
C., but finally it comes up to a point where it
This is a very slow process. After the first multiplies equally well at 250 C. and at 360 C.
five passages at 250 C., the yield of virus, when After selection of special plaque progeny,
all the cells were destroyed, was approximately even higher propagation was obtained at 250
100 times less than that obtained at the higher C. than at 360 C.
temperatures.
The same thing occurred for Type 3. Although
the Type 3 Leon strain had much Incidentally, I should point out that, when-
more
Selective Enrichment of 250C Variant by Serial Propagation at Progressively Lower Temperatures
Types 2 and 3 Attenuated Polioviruses
Type 2 -P712, Ch,2ab
S 36 3 253
36- 6 36 25
Type 3-Leon, 12a,b
25
o
7-
33 3 6
V25 Z
P IO PS
P 20 20 P 26
36- 30' 25-
Type 3- Glenn
36
E - 8 36 S2 Só ; 20 ,
P -,
I-CPE titer rt36C clt 8doys, Partial CPE titer at 25C at 14 days
*Complet .
Fio. 2