LIVE POLIO IRUS VACCINES

518
Efficacy-Field Evidence
in the population of the four experimental and
neighboring regions was investigated and repeated
investigations on the spread of wild
polioviruses (and other enteroviruses) were conducted
in several Czech and Slovak regions. The
main attention was paid to relations between
the amount of detected strains and the poliomyelitis
morbidity*. The results, obtained before
the usual onset and at the peak of the usual
polio season (June-September), are of particular
importance. From the results, discussed in
greater detail elsewhere (Burian, Vojtová and
others), I should like to demonstrate the following
main facts shown on two maps (Figures 5
and 6):
(a) Repeated investigations in four regions,
where in the winter of 1958-1959 the live vaccine
was administered (Fig. 5), revealed that attenuated
viruses disappear relatively rapidly from
the population. Isolated viruses, if detected
later in non-vaccinated individuals (white circles
on the map), were most probably wild viruses
imported to these regions from elsewhere, or
wild viruses occurring in the non-vaccinated
part of the population. (It must be emphasized
that the first field trial with the live vaccine was
conducted in a relatively small part of the population-in
less than 50 per cent of children aged
two to eight years). The polio-morbidity in
these four regions (black squares on the map;
one square stands for one case of poliomyelitis)
does not have any peculiar features.
(b) Very important results are shown on the
map summarizing the results of two investigations
of the poliovirus spread in Czechoslovakia
in 1959 during June (A) and September (B),
and which gives also the number of cases of
poliomyelitis in the second half of 1959 (Fig.
6). The results indicate that in regions neighboring
upon those where the live vaccine was
administered, the incidence of polioviruses was
low and that thus, most probably, these viruses
did not penetrate into neighboring regions. (It
must also be taken into account that the vaccination
was carried out in winter). If later there
was a higher incidence of viruses in some localities
(such as in the Gottwaldov region), this
* Specimens of feces, proportional to the population
densitv, were collected by random sampling,
predominantly from children. In child communities,
never more than two specimens were taken from one
community.
was more probably due to the penetration of
wild viruses from neighboring Slovak regions,
particularly the Zilina region, which is very
close to the Gottwaldov region. (It is interesting
to note that in 1959 there was an extensive
poliomyelitis epidemic in neighboring Hungary,
which borders on Slovakia along the entire
frontier.)
The most important conclusion from these
investigations is that, when there was a higher
incidence of polioviruses in the population,
which had been practically evenly vaccinated
with the inactivated vaccine, there was also a
higher incidence of poliomyelitis. In other
words, we may say that not even the previous
high vaccination rate with inactivated vaccine
was able to prevent the spread of polioviruses
and that to a certain degree, we have to rely on
chance whether an unexpected spread of viruses
will occur or not. If we add to this the defects
of seroimmunity, it is evident why in 1959 there
was a substantially higher morbidity in Slovakia,
as shown in Fig. 2 and why we considered
the future epidemiological prognosis of poliomyelitis
in our country uncertain.*
The main purpose of my report was to give an
idea of the trend of our deliberations and to
demonstrate at least some fundamental facts
on which we based our decision to use the live
vaccine for mass vaccination. I think that our
results indicated clearly the necessity to improve
the state of immunity of our most susceptible
population. A comparison of the results of the
first field trial with the live vaccine with those
after the administration of a fourth dose of
inactivated vaccine on a mass scale, however,
revealed also the method of how to achieve
this improvement most expediently. I have tried
to summarize the balance of our deliberations
on the advantages of either method in Table 6.
The objection could certainly be raised that
our decision was premature. I dare not, however,
answer the second aspect of this objection,
and I doubt that anybody will be able to do so.
It is my opinion that it would be much more
difficult to explain to our people in the case
of an epidemic, why we did not undertake every-
* The results assembled during the first few months
of 1960 confirmed to a certain extent that these fears
were justified. The number of patients between
1 January 1960 and 28 March 1960 was, as comPared
with the same period in 1959, three times greater
(66:22), and several small local epidemics occurred.