LIVE POLIO IRUS VACCINES

Use of Sabin's Live Poliovirus Vaccine in Mexico
401
time, in a manner comparable to that achieved in
Toluca and previously described by Dr. Sabin.
The administration of the vaccine under the
conditions described in Mexico City and Guadalajara
over a period of several weeks, including
only a fraction of the susceptible population (17
per cent in Mexico City and 30 per cent in the
City of Guadalajara), failed to immunize a certain
proportion of the vaccinated children and did
not influence the dissemination of the naturally
occurring paralytogenic strains, as shown by the
subsequent course of the Type 1 epidemic encountered
in these two cities at the time of vaccination.
Although it would be difficult to calculate the
real effectiveness of the vaccine under the conditions
of the present studies, it should be emphasized,
nevertheless, that on the basis of the population
at risk, there was a striking difference between
the number of expected cases and the number
of observed cases in the vaccinated children,
which was particularly evident in the cities of
Monterrey and Puebla. Thus, it may be assumed
that the oral vaccine was effective in preventing
a large number of paralytic cases.
ACKNOWLEDGMENTS
The authors wish to acknowledge the cooperation
of the staff of the Ministry of Public Health
and Welfare of Mexico and of the staff of the
Mexican Institute of Social Security, particularly
Drs. Juan Assael and Samuel Inclán.