LIVE POLIO IRUS VACCINES

136
Safety-Field Evidence of Safety
from several stool samples from both patients
and no serological evidence of poliovirus infection
was found. Hence, the morbidity rate is
probably half of that recorded in Fig. 4.
With regard to the remarks made by Professor
Dick3 at the first Conference, we hesitate to put
forward our opinion that the two Type 2 cases
are definitely not due to the introduction of the
vaccine into the population. The types of vaccine
have been administered in the order Type
1-Type 3-Type 2, the Type 2 vaccine having
been fed in December. Both cases, however, occurred
in October, two months prior to the administration
of the Type 2 vaccine!
Hence, all trials, particularly the three made
during the years 1958 and 1959 with an exceptionally
low incidence of poliomyelitis, clearly
show that the introduction of the vaccine into
the population has not resulted in the occurrence
of clinical poliomyelitis. You will note that there
has not been a single case of poliomyelitis in the
Leiden region for two years, from September
1957 to October 1959.
The incidence of poliovirus infection in the
different regions as determined by virological
examination of patients, irrespective of the
character of the clinical syndrome, is presented
in Fig. 5, which shows that in none of the years
in which oral vaccine has been administered there
has been a significant increase in the incidence of
poliovirus infections in the Leiden region as compared
with the other regions. On the contrary,
r
BELGIUM -
FIc. 2. Map of The Netherlands, with indication of the study areas.