LIVE POLIO IRUS VACCINES

Susceptibility of Newborn Infants to Infection with Poliovirus Strains 313
age. The D 2 . 3 ID50 will be useful as the more accurate
basis for comparison with other vaccine
candidates and with other age groups. The D2_ 3
ID,, is probably the measure needed in actual
practice since a vaccine can hardly be acceptable
as an immunizing tool which is not effective in at
least 90 per cent of those receiving it. The 30-
day-old babies were included to permit comparison
(using Type 1) with somewhat older children,
and further comparison is valid with our previous
experience with still older children 8 since
the material, techniques, and investigative personnel
involved were essentially the same. Our
aim, therefore, was to complete Table 6.
TABLE 6. INFECTIVITY ENDPOINTS OF "SABIN
VACCINE" VIRUS STRAINS IN CHILDREN OF
DIFFERENT AGES
Virus
Infectivity endpointa
typ. Age I DS0 I D0O
2-3 daya
1 30"
> 1 year* < 10 6 < 10.
2 - days
2 > 1 year < 105' < 105.:
2 - da."*
3 1 year* < 4