LIVE POLIO IRUS VACCINES

15. USE OF SABIN'S LIVE POLIOVIRUS VACCINE IN MEXICO.
RESULTS OF A LARGE.SCALE TRIAL
MANUEL RAMOS ALVAREZ, M.D., MIGUEL E. BUSTAMANTE, M.D.,
AND RAFAEL ALVAREZ ALBA, M.D.*
The Children's Hospital, Mexico City, Mexico; Ministry of Public Health and
Welfare; and the Mexican Institute of Social Security
DR. RAMOS ALVAREZ (presenting the paper):
Studies with Sabin's live poliovirus vaccine have
been conducted in Mexico during the last three
years.
In 1957, carefully controlled laboratory and
clinical observations were carried out on 181
children, mostly under three years of age, living
in an orphanage in Mexico City to whom various
doses of the attenuated strains separately or in
mixtures were fed. In February 1958, investigations
were extended to 2,800 children under six
years of age living in 28 nurseries distributed in
different sections of Mexico City, to whom the
vaccine strains were fed separately at three to
four-week intervals in the recommended order
(Type 1, 3, and 2) in concentrations of approximately
105.6 to 105'9 TCD 50 for each type. In addition,
clinical observations were also made on
7,000 contacts of these 2,800 children. No untoward
reactions were observed in any of the vaccinated
children or in any of their contacts.
Serologic studies on serum samples obtained
from a group of these children before and after
vaccination, showed the following antibody conversion
rates: among 42 children negative for
Type 1, 74 per cent converted to positive; among
52 children negative for Type 2, 77 per cent converted
to positive; and among 37 children negative
for Type 3, 67 per cent converted to positive.
The results of these preliminary studies, as well
as the results obtained by other investigators
working with the same strains, showed the innocuity
of the vaccine and its immunogenic properties.
Accordingly, the Ministry of Health of
Mexico approved a large-scale vaccination pro-
* The following persons also cooperated in different
parts of this work: Dr. Luis Rangel Rivera, Dr.
Arturo González Durán, Otila Mayés, Q.F., and Lucía
Bustamante, Q.F., of the Children's Hospital, Mexico
City.
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gram to be carried out at the end of 1958. A
preliminary report of this trial was presented at
the First Conference last year. The present report
is intended to give a more detailed description
of the conditions under which the campaign
took place and the results obtained.
The administration of the vaccine was carried
out on a voluntary basis in four different cities:
Mexico City in the central part of the country;
the City of Guadalajara, located approximately
400 miles northwest of Mexico City; the City of
Monterrey, in the nothern part of the country;
and the City of Puebla, approximately 100 miles
south of Mexico City. It was limited to children
under five years of age, who are the most susceptible
population group according to previous
laboratory and epidemiological observations.
A serological survey of the population in three
of the cities under study just before the beginning
of the vaccination program (Fig. 1), indicated
that immunity to poliomyelitis is naturally acquired
during the first four years of life. Eighty
to 90 per cent of the children of four years of age
showed antibodies to all three types of poliovirus.
The available data in these cities for the past
five years indicate the following:
(1) Major outbreaks of poliomyelitis occurred
every two years, with summer rises varying
somewhat according to the year, sometimes
as early as March, and sometimes as late as June
or July.
(2) Mexico City, with a total population of
4,500,000 people, had an average of 349 paralytic
cases per year; the City of Guadalajara, with a
population of approximately 700,000, had an
average of 132 cases per year; the City of Monterrey,
with a population of 600,000, had an average
of 72 cases; and the City of Puebla, with a popu-