LIVE POLIO IRUS VACCINES

444
Effcaey-Field Evidence
44 EfiayFedEiec
poliovirus throughout the community. On the
basis of the results obtained in approximately
100 individuals who were bled before three to
four weeks, and again six to seven weeks, after
oral vaccination, we have no cause to regret this
decision for the high conversion rates were not
influenced by the increased time intervals, although
they might well have been had we been
using a less effective antigen.
The high conversion rates of over 90 per cent
observed by us for both Types 1 and 3 in individuals
lacking measurable antibodies to both these
types would lead one to doubt that there was
significant interference between these two vaccine
poliovirus types or between the vaccine
strains used, and the enterovirus usually presumed
to be present in subtropical areas.
The reduced capacity of the Type 2 vaccine
strain used to produce human infection, as evidenced
by the lower conversion rates, is unexplained,
but it raises important questions concerning
the correlation of animal and human
virulence.
The data on conversion rates obtained here
and reported elsewhere by others, suggest that
the administration of trivalent vaccine of this
antigenic potency will be a public health tool
that is superior to the sequential feeding of
monovalent vaccine of comparable antigenicity.
In the U.S.A., there is much experience to indicate
that the percentage of persons satisfactorily
completing an immunization or other nonemergency
health procedure, which requires repeated
revisits to the physician or clinic, varies
inversely with the number of visits required to
complete the immunization or treatment. Much
evidence would be necessary to show that any
theoretical superiority of sequential feeding of
oral polio vaccine compensates for the increasing
delinquency. It is probable that refeeding of
the trivalent vaccine will be recommended to
obtain maximal immunity for all individuals.
Failure of an individual to receive this second
dose, which is primarily used to insure Type 2
immunity, is of much less individual and public
health significance than would be the failure to
get either one or more of the monovalent strains
given in sequential feedings. Also, to be considered
in the trivalent versus monovalent question
are such factors as the convenience of the
public, economy of time of the professional staffs,
and the length of time required to protect the
maximal number of the population in the shortest
period of time.
SUMMARY
1. A presentation of preliminary data of a
field trial in Dade County, Florida, in which
412,000 persons were vaccinated with a single
oral dose of Cox-Lederle trivalent attenuated
poliovirus vaccine, is given.
2. Poliovirus neutralizing antibody studies
have been reported on 594 individuals lacking
antibodies to one or more types of poliovirus
before oral vaccination. The efficacy of the
vaccine, as measured by its ability to lead to
antibody production in these individuals, was
95 per cent for Type 1, 97 per cent for Type 3,
and 78 per cent for Type 2.
3. Our experiences lead us to believe that
valid large-scale field trials of oral polio vaccine
can and should be conducted in the social, geographic,
and age groups in which its ultimate
utilization is planned.
ACKNOWLEDGMENTS
Acknowledgment is made to the U. S. Public
Health Service and to Dr. M. Martins da Silva
of the Pan American Health Organization, for
assistance given.