LIVE POLIO IRUS VACCINES

Vaccination with CHAT Strain Type 1 Polio Virus in Leopoldville
473
the highest levels of significant protection were
those in which Type 1 viruses were circulating at
some time during this period in addition to Type
3. It is also possible, of course that Type 1
immunity partially protects against Type 3
poliomyelitis.
SUMMARY
Seventy-five thousand African children under
the age of five years have been vaccinated in
Leopoldville, Belgian Congo with CHAT Type 1
attenuated virus beginning in August 1958. Approximately
46,000 of these children are in the
highly susceptible group of which 41,000 had
been vaccinated as of 30 April 1960. During
this period there has been an epidemic of Type 1
paralytic poliomyelitis, followed by a smaller
Type 3 epidemic. A six-month period has passed
without the isolation of Type 1 virus from patients
with paralytic poliomyelitis. Cases in
vaccinated individuals did not occur during the
period immediately after vaccination more frequently
than would be expected by chance.
Virus strains isolated from vaccinated and nonvaccinated
cases in Leopoldville were shown in
the laboratory to differ from CHAT virus and
its known human passages in at least two
chlaracteristics.
The efficacy of vaccination computed as closely
as possible appeared to be on the order of 67
per cent. Where poliomyelitis was most exclusively
caused by Type 3 virus, there was the least
difference in incidence between expected and
observed number of cases in vaccinees.
ACKNOWLEDGMENTS
We wish to express our thanks to Dr. Ghyssels
and Dr. Jourdain of the Princess Astrid Institute
of Tropical Medicine in Leopoldville, and to
Suzanne Richardson of The Wistar Institute.
REFERENCES
1. Lebrun, A., Cerf, J., Gelfand, H. M., Courtois,
G., Plotkin, Stanley A., and Koprowski, H.:
Vaccination with the CHAT strain of Type 1
attenuated poliomyelitis virus in Leopoldville,
Belgian Congo. 1. Description of the city,
its history of poliomyelitis, and the plan of
the vaccination campaign. Bull. Wld. Health
Org. 22: 203-213, 1960.
2. Plotkin, Stanley A., Lebrun, A., and Koprowski,
H.: Vaccination with the CHAT strain of
Type 1 attenuated poliomyelitis virus in Leopoldville,
Belgian Congo. 2. Studies of the
safety and efficacy of vaccination. Bull. Wld.
Health Org. 22: 215-234, 1960.