LIVE POLIO IRUS VACCINES

192 Safety-Field Evidence of Safety
TABLE 2.
MOUSE PATHOGENICITY OF POLIOVIRUS TYPE 2 FROM HEALTHY LOOKING INFANTS UNDER
Two YEARS OLD iN TOKYO
Name of Intracerebral Intraspinal
Strain Inocu.lation Inoculation TCID,,
SK-1 9/26* 16/20 106-0
SK-2 1/29 9/15 105.7
SK-8 8/28 16/18 106.0
SK-40 4/30 16/18 106.5
SK-50t 0/30 9/27 107.0
SK-53 6/30 16/20 106'3
Control Type 2 poliovirus strain isolated from a
paralytic polio patient 23/27 106.0-7.0
* Numerator: number of deaths.
Denominator: number of inoculated mice.
t Inoculated intraspinally into 2 cynomolgus monkeys, one suffering from paralytic polio and the other
remaining well.
TABLE 3. VIRUS ISOLATIONS FROM STOOLS ample) and which are mixed in nature with the
OF ALL INHABITANTS INCLUDING POLIO highly virulent strains.
CASES IN TATAKI VILLAGE, EHIME PREFEC- Needless to say, in order to match the epi-
TURE, 1956
demiological features in the endemic area, a
All Healthy strain of extremely low virulence may be made
Age (years) Polio Cases Inhabitants available as a vaccine, provided it is proven to
0 - 1 5/19* (5) 7/22 be capable of immunizing the subject, of being
2- 3 5/1] (2) 10/2 genetically stable, and of not becoming virulent
4- 5 5/11 8/26 through serial passage from man to man. Fur-
6 - 7 2/8 (1) 3/40 thermore, it is highly possible to replace the viru-
8- 9 0/3 C/41 lent wild strain by such a low virulent strain in
10 -1 1/11/: the endemic area. In 1954, at the Third Inter-
12 1-- 1/1 0/23 national Poliomyelitis Conference in Rome, it
14 15 1/1 0/10 was reported that two strains, namely B-34 (iso-
16 -- 20 £/42
2?1 - 20 u/60 lated from the father of a polio patient in Tokyo)
31- 40 ,/ -, and Lansing, had become avirulent for mice by
41- 50 0/50 the IC route through passage in tissue culture;
50- over 0/S3 later, however, on the advice of Dr. Sabin, viru-
Unknown 0 lence tests by the IS route showed that the strains
were not yet completely avirulent. During the
Total 55 (513 experiments on poliovirus mutation problems, the
: Numerator: No. of positive isolations. mit+- strain, derived from the wild strain MEF-1,
Denominator: No. of test samples.
was decreased in virulence to the point of caus-
( ): No. of other viruses such as Coxsackie, Echo
and Adenoviruses.
ing only one death out of 50 mice inoculated by