LIVE POLIO IRUS VACCINES

446
Efficacy-Field Evidence
446 Efficacy-Field Evidence
tive epidemiological observations on a sporadically
occurring infection.
quota sampling technique.
This report describes plans for the continuing
study necessary to evaluate efficacy and safety of
the vaccine to the individual and to the community,
with observations covering a period of initial specimen.
from one to over three months following the
administration of the vaccine to more than
400,000 people. Large numbers took the vaccine
in the early weeks of the study, and over 200,000
have been observed for an average of three
months following vaccination.
years.
The Cox-Lederle trivalent vaccine was used
exclusively throughout the study.
THE SETTING FOR THE STUDY
Dade County includes Miami, Miami Beach, 25
other urban municipalities, broad suburban areas,
and a comparatively small rural region. It has a
subtropical climate. The overall socio-economic
level is relatively high. Its population has been
increasing at approximately 7 per cent per year.
Accurate population figures will be available only
upon completion of the 1960 census. However,
as of 1 February of this year, it was estimated
that there were 920,000 permanent residents,
of whom approximately 560,000 (60 percent) are
less than 40 years of age. Thirteen per cent of
the population is non-white.
Paralytic poliomyelitis in Dade County is an
endemic disease occurring in all seasons. In
most years, the highest incidence is in August,
September, and October (Table 1). Annual
paralytic attack rates have varied widely from
a low of 0.8 cases per 100,000 in 1957, to a high
for recent years of 16.4 in 1954. The case rate in
1959 was 4.2 per 100,000. In 1960, for the four
months under consideration, the case rate was 2.3
per 100,000 person years. Deaths for the same
years numbered one in 1957, eight in 1954, three
in 1959, and one in 1960.
Immediately prior to the vaccination program,
the immunization status of the entire population
was estimated through both interview and
serologic sampling technics. The data are being
analyzed in terms of age, sex, race, education,
socio-economic rating, and prior Salk vaccination
history. The study population included a total
of 1,499 households, with 4,630 people randomly
selected from the community through use of a
Blood specimens
were obtained from a subsample of 1,286 persons.
A second blood specimen is being collected
one month following the termination of the vaccination
program, or about four months after the
Preliminary tabulations show
that the approximate percentages of people who
have had no Salk vaccine varied from about 15
per cent for those less than five years, 8 per cent
for those five to 20 years, 30 per cent for those
20 to 40 years to 67 per cent for those over 40
In the same age groups, the percentages
of those who have had three or more Salk inoculations
were 56, 83, 45, and 16, respectively.
Those most adequately immunized, therefore,
were those of elementary through high school age.
The record was more favorable in all ages for
those in the higher socio-economic class and poorest
in the lower socio-economic level.
Identifying data for each orally vaccinated
person are being recorded permanently on IBM
punch cards. These will serve as the check list
for the verification of vaccination history for all
subsequent central nervous system infections.
These alphabetized records are not yet available
and to date vaccination histories are based on
the statement of patients and confirmation of
clinic dates. Data drawn from these vaccination
records, from the immunization survey, and from
the 1960 population census, will clearly define the
various segments of the population by Salk and
by oral polio vaccination status.
SURVEILLANCE PROCEDURES
The staff of the Dade County Department of
Public Health includes a full-time epidemiologist.
For this study the epidemiology staff was augmented
by an additional epidemiologist and a
nurse. In recent years, the epidemiologist has
personally investigated all known or suspect cases
of central nervous system infection. Reporting of
such diseases by practicing physicians has be
come relatively prompt and adequate. Moreover,
in the hospital associated with the medical school
and in the one community hospital to which
recognized polio cases are admitted, infections of
the central nervous system are receiving special
study. The epidemiologist has worked closely
with these and other clinical and research groups.
There is an unusually favorable and close co-