LIVE POLIO IRUS VACCINES

16. STUDIES ON LIVE POLIOVIRUS VACCINE IN JAPAN
MASAMI KITAOKA, M.D.
WHO Regional Polio Center, Tokyo National Institute of Health, Tokyo, Japan
DR. KITAOKA: According to the recommendation
of the WHO Expert Committee on Poliomyelitis,
Geneva, 1957, formaldehyde inactivated
vaccine (Salk type) has been prepared in my
laboratory on a small scale. Four private manufacturers
of biological products have now started
to make an adequate amount of the vaccine to
immunize the community against poliomyelitis
in endemic areas, especially infants, although
some amount of the vaccine is still imported for
this purpose. At the same time, the WHO Expert
Committee recommended that further investigation
be carried out on the live attenuated
vaccine in the laboratory, as well as in field trials.
In reviewing the epidemiology 1 of poliomyelitis
in Japan, our attention should be focused more
on the live attenuated vaccine than on the Salk
vaccine, taking the following into account: (1)
the age distribution of the incidence of paralytic
polio is almost limited to the < 1 to 3 year-old
group (508/608=83.8 per cent), especially
affecting the children < 1 to 1 year-old (376/-
608=61.8 per cent (Table 1); (2) any type of
poliovirus could be isolated from the stools of
healthy-looking children; in the summer of 1956,
for example, six Type 2 polioviruses were isolated
from six infants aged two months to two
years at the Infant Home in Tokyo, where no case
of paralytic polio has been recognized in the
past several years (Table 2); (3) not all of these
six strains proved to have the same high paralytogenic
properties, but some, for example the
SK-50 strain, proved to be of very low virulence
for mice and monkeys after their inoculation by
intracerebral (IC) and intraspinal (IS) routes,
as shown in the table; (4) the blood level of
neutralizing antibodies in children was found
generally to reach the maximum in titer against
all types of poliovirus without manifest infection
in the five-year age group; and (5) under poor
sanitary conditions, when a polio epidemic caused
by Type 1 poliovirus broke out in 1956 in Tataki
village, almost all infections were in children
under seven (Table 3).
From the foregoing, it can be presumed that
many children reared in the endemic area are
acquiring immunity against polio, following subclinical
infection with such a strain of low paralytogenic
properties of varying degree, which
could multiply in the intestines the same as a
saprophytic microorganism (E. coli., for ex-
TABLE 1. AGE AND SEX DISTRIBUTION OF POLIO CASE INCIDENCE IN 16 CITIES AND TOWNS IN
JAPAN, 1956-1958
Age