LIVE POLIO IRUS VACCINES

Course of Mass Immunization in USSR with Vaccine from Sabin's Strains
421
In the course of observations on vaccine virus
excretion during revaccination it was possible
to establish that in contrast to the killed Salk
vaccine, the live poliovirus vaccine produced not
only serological, but to a certain extent, also
local immunity, i.e., immunological resistance of
cells of the alimentary tract. This may result in
progressive reduction of poliovirus circulation
among the population.
The problems associated with the dynamics of
the development of local immunological resistance
to poliovirus demand, however, further
study and more precise definition. It is necessary
also to solve the problem of providing continuous
immunization considering possible complete
disappearance of latent poliovirus strains.
We believe that for this purpose children of 0
to 3 years of age should be immunized with live
vaccine annually.
3. Virus carriage and contact transmission.
As evidenced by numerous observations, including
those performed at our Institute, oral immunization
with live poliovaccine is accompanied by
more or less protracted excretion of vaccine
strains. The duration of virus excretion in
children without antibodies is approximately
twice as long as in those possessing them. In the
environment of the vaccinees (under conditions of
family contact) all persons susceptible to poliomyelitis
pick up vaccine within a very short
time and become immunized latently. No untoward
reactions could be noted in connection with
virus carriage and transmission of vaccine viruses
by contact. Quite the contrary, it can be regarded
as established that virus carriage and
contact transmission during mass vaccination
represent an exceptionally favorable factor conducive
to all-round and more rapid immunization
within families and communities.
4. Interference. In oral immunization with
live poliovirus vaccine the phenomenon of interference
between wild and vaccine poliovirus
strains, between non-poliomyelitis enteroviruses
(ECHO and Coxsackie groups) and live vaccine
strains, and also interference between individual
types in live vaccine acquire special importance.
As a result of extensive investigations it has
been found that interference between vaccine
and other enteroviruses occurs under various
epidemiological conditions, with frequency in
different months of the year. Winter months are,
apparently, most advantageous for vaccination.
The data obtained enable us to draw a preliminary
conclusion to the effect that most instances
of oral immunization failures are due to
the influence of interference upon the vaccination
process. The interference may, probably,
be overcome by particularly massive vaccinations
(with involvement of no less than 50 per cent of
the susceptible population) and by repeated vaccinations
over a period of one to three years.
Furthermore, complete study of patterns
governing the interference between enteroviruses
and vaccine strains of poliovirus is urgent.
5. Epidemiological effectiveness of mass immunization
with live poliovirus vaccine. This
was established for the first time in the Soviet
Union on the basis of information gathered in
1959, the latter discussed in detail in our Report
No. 2 (Moscow, 1960). Particularly convincing
was the reduction in poliomyelitis incidence in
Estonia and Lithuania, where triple immunization
with live vaccine was carried out before the
summer poliomyelitis season, as well as in
Karaganda and in the Moscow region where conditions
favored comparisons between the incidence
in the vaccinated and the unvaccinated
groups. In the first three months of 1960, a
satisfactory situation with regard to poliomyelitis
continued to prevail in Estonia, Lithuania, and
other areas which were subject to observations
(see Tables 5 and 6).
In Estonia during the last 12 months there
were only 12 poliomyelitis cases. These were
recorded only during the first six months, and the
last six months were completely free from poliomyelitis.
An unusually low number of poliomyelitis
cases is recorded after vaccination in
Lithuania. In Moscow, where every fourth
inhabitant has been vaccinated (or over 90 per
cent of the population under 20 years of age)
a sharp reduction in poliomyelitis incidence is
being observed. In all areas where vaccinations
with live vaccine have been completed, the number
of poliomyelitis cases is rapidly decreasing.
Observations in carefully controlled trials indicated
very high epidemiologic effectiveness of
mass immunizations with live poliovirus vaccine
(9.5-20.5-fold reduction in paralytic poliomyelitis
incidence).
Of particular interest are materials covering the
1959 vaccination program in Tashkent. Simul-