LIVE POLIO IRUS VACCINES

Recent Experience with Lederle Trivalent Oral Poliomyelitis Vaccine 339
per cent. Conversion rates of this order were
also obtained in the triple negatives in a similar
short span of time, but comparable conversion
rates were not attained in the Salk vaccine study
of Gelfand et al., 3 until primary immunization
liad been followed by a booster injection more
than 11 months later. The purpose here is not
to detract from the good that the Salk vaccine
has accomplished, but only to compare the results
given by a new method of vaccination with
those of the old-for it should be remembered
that we here are concerned with matters of life
and limb as well as with pride and treasure.
The relatively poorer response rate to the Type
2 strain in the present trivalent vaccine can certainly
be improved by additional research and
development. However, the magnitude of its
deficiency must be judged in the light of our
knowledge regarding the relative minor import.
ance of Type 2 virus as a cause of paralytic
poliomyelitis. The ideal poliomyelitis vaccine is
still a thing of the future, perhaps the somewhat
distant future, but this need not and should not
mean that progress must await perfection.
Many problems still remain in the field of oral
poliovirus vaccination. It is the obvious hope of
everyone that a single feeding may be all that is
required. However, in areas where maternal
antibody levels are high, repeated feedings of
vaccine may be necessary in the newborn and
very young. Optimum conditions regarding the
relationship of diet and the physiologic state of
the digestive tract are largely unknown. The
duration of immunity has not been established,
and this may be difficult to do in certain areas
because of the frequent opportunities for natural
booster exposures after vaccination. Until
adequate supplies of vaccine are available, so
that an organization equipped for mass application
can move quickly into an epidemic area, it
will not be known how effective oral vaccination
can be in curbing an outbreak of poliomyelitis.
Everyone agrees as to the desirability of
strain markers and identifying characteristics,
but there is considerably less agreement as to
the significance and stability of these signs.
These are but some of the more obvious and important
problems that await solution, but they
are secondary to the main problem of getting
an effective tool into the hands of those who can
and wish to put it to work.
SUMMARY
The serologic responses of 1,416 volunteers
who received trivalent oral poliovirus vaccine are
presented and discussed. A single vaccine dose,
consisting of approximately 106 ' 1 tissue-culture
doses (1,200,000 TCD 50 ) of each of the three
types of attenuated poliovirus suspended in 2 ml.
of fluid was administered.
In the three groups which constituted the study
population, the conversion rates from seronegative
to seropositive status ranged from 91 to 100
per cent for Type 1 poliovirus; from 68 to 75
per cent for Type 2, and 93 to 97 per cent for
Type 3. Eighty-eight per cent of total of 948 seronegatives
responded to a single oral vaccination.
One of the study groups included 154 persons
who had received three or more injections of
Salk vaccine. Collectively they represented 52
seronegatives, all but one of which responded to
oral vaccination.
Response rates to the trivalent oral poliovirus
vaccine were comparable to response rates to the
same strains fed separately.
REFERENCES
1. Cox, H. R., Cabasso, V. J., Markham, F. S.,
Moses, M. J., Moyer, A. W., Roca-García, M.,
and Ruegsegger, J. M.: Immunological response
to trivalent oral poliomyelitis vaccine.
Brit. M. J. 2: 591-597 (October 3) 1959.
2. Embil, Jr., J., Castellanos, A., and Jiménez,
R. M.: A clinical and serological study of the
response of Cuban children to oral vaccination
with attenuated poliovirus vaccines. In: Live
Poliovirus Vaccines, First International Con-
Jerence. Scient. Pub. no. 44 of the Pan American
Health Organization, pp. 593-617, 1959.
3. Gelfand, H. M., LeBlanc, D. R., Fox, J. P..
and Potash, L.: Studies on the development of
natural immunity to poliomyelitis in Louisiana.
III. Serologic response to commercially produced
"Salk Vaccine" of children totally or
partially susceptible to poliovirus infection.
Am. J. Hyg. 70: 303-311 (November) 1959.
4. U. S. Dept. of Health, Education and Welfare,