LIVE POLIO IRUS VACCINES

454
Efficacy-Field Evidence
It is noted that there were five cases in the
recently vaccinated giving a case rate of 15.6 per
100,000, and none in the vaccinated after an interval
adequate to permit the development of antibodies.
In the unvaccinated less than 40 years of
age, the case rate was 1.0 per 100,000, and in
those 40 years and over, 0.8 per 100,000 person
years. The case rates are to be compared with
illustrative rates for Dade County of 4.2 per
100,000 total population in 1959, of 0.8 in 1957
(a year of low incidence), and of 16.4 in 1954 (a
year of high incidence). Thus the case rate in
the recently vaccinated compares with that for
the population as a whole observed in a year of
high incidence. The lack of cases in the 55,000
person years of experience of the orally vaccinated
is encouraging.
Time relationships are of particular importance.
The intervals between the taking of the
vaccine and onset of symptoms were respectively
7, 9, 9, 13, and 14 days. Coincidental cases would
be expected to have onsets distributed evenly at
least for the first two weeks following vaccination.
A chance grouping of onsets of all cases within
the second week following vaccination would be
improbable. In the experience with the live virus
vaccine in the USSR, there are reports that onsets
of illness in paralytic cases up to and including
10 days following oral vaccination were interpreted
as cases probably related to pre-existing
infection due to wild virus. Although these
would be expected to occur in any large-scale
use, cases of this type were not discussed in the
official presentation from the USSR. We can
therefore only emphasize the importance of records
that show both the occurrence of paralytic
polio in vaccinees from the day of vaccination to
onset of illness, as well as complete reports of
cases occurring in the comparable unvaccinated
group. Data of this kind are obviously required.
There were two cases in 1960 in the orally
unvaccinated. As noted in the case reports in
the appendix, one occurred in a child of a rural
family, no member of which had taken oral vaccine
and in which the probability of contact with
the vaccine virus was relatively remote. The
other was the fulminating fatal case whose wife
and child had taken oral vaccine one month
earlier. The course of the disease spoke for infection
with a highly virulent virus. If these
are accepted as coincidental infections and
disease, the evidence indicates the safety of an
oral polio vaccination program to contacts and
the community.
Of the seven cases, poliovirus was isolated from
four, all yielding Type 3 virus and two of these
Type 1 also. In two cases findings are pending.
In the fatal case no feces were collected.
None of the seven cases had had a full course
of Salk vaccination. Two had been inoculated
twice. The child of two received the last dose 18
months prior to onset. The adult male had taken
them "about five years ago."
The one suspect case in which diagnosis is still
undetermined is a male 20 years of age. He noted
malaise, headache, fever and difficulty in swallowing
with onset 11 days after taking oral vaccine.
His symptoms improved but the gag reflex
is still absent. He had had no Salk vaccine.
This patient has some neuromuscular congenital
defects.
COMMENT
At this time we are able to present only very
early and obviously incomplete observations.
Final evaluation will need to include the results
of marker studies and serological findings,
neither of which is at hand. Thus our impressions
must be based chiefly on epidemiological
findings. The observations which impress us as
being of greatest significance include:
1. There was a ready acceptance in Dade
County of a living oral poliovirus vaccine by
412,000 of the population.
2. Significant immediate reactions to oral polio
vaccination were not observed.
3. The usual incidence of aseptic meningitis
and encephalitis noted in the previous year continued
throughout the trial period without significant
change.
4. There was no evidence of any significant
association between attenuated vaccine virus and
the 29 currently accepted cases of non-bacterial,
non-paralytic infections of the central nervous
system. Four of these 1960 cases occurred prior
to the field trial.
5. There was substantial evidence of safety
to contacts in the presence of an extensive use of
oral polio vaccine.