LIVE POLIO IRUS VACCINES

Experimental Infection with CHATAttenuated Poliovirus in Premature Infants 291
that the half life of maternal poliomyelitis antibodies
in premature infants appears to be about
23 days).
Readministration of Virus. When the same
dose of the same virus was given a second time
three to five months after birth to infants that
liad previously been infected and had had a positive
antibody response (Table 6), in other words,
successfully vaccinated, the response was as ex-
pected. Such infants were resistant to reinfecttion:
only two of six infants were detectably reinfected,
and these two infants excreted virus for
less than five days, compared with an average
excretion of over four weeks in the six infants
after the first feeding. Three of the six infants
had a rise in antibody titer.
In contrast the highly interesting group of
five infants. who although infected had not had
128
*Successfully
Vacc.
64
\
OUnsuccessfully Vace,
0Unvacc. Control
Y
C
16
8
\
e
(48)
o
FIG. 1.
Antibodv levels at intervals after birth in successfully and unsuccessfully vaccinated premature
infants and in unvaccinated control infants.