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(b) the absolute and relative efficacy of three different
British products, and
(c) the extent to which the protection afforded by these
three British products agrees with laboratory tests of their
potency.
Previous experience has shown certain fallacies in comparing
results in inoculated and uninoculated groups of children; and,
in order that the investigation will be completely objective, no one
actively engaged in the investigation will know which vaccine any
individual child received.
Preliminary Work—Propaganda.
The most effective method of obtaining volunteers is for health
visitors to explain the scheme to mothers at welfare centres and
during routine visits. Pamphlets explaining the scheme, with
detachable consent forms, will be distributed to mothers, and each
general medical practitioner in the area will receive a letter explaining
the scheme and asking for his co¬operation. Posters will be
exhibited in each health centre and day nursery. The need for
additional propaganda will depend on the response from the
sources mentioned above.
After receipt of the consent forms the volunteer children
will be divided into the necessary age and sex groups, and mothers
will be given letters of appointment, etc.
Children Eligible.
In the first instance only children aged 6 to 18 months will be
accepted, as it is in this age-group that most deaths occur. These
children must not have had whooping cough, nor must they have
been inoculated against it. If sufficient volunteers do not come
forward, the age limit may be raised.
Course of Injections.
The course consists of three injections with an interval of one
month between each. These injections do not interfere with
diphtheria immunisation; in fact, there is no reason why the two
courses of inoculation should not be carried out at or about the
same time.
Follow-Up.
For a period of two years after inoculation each child who has
completed the course of inoculations will be visited monthly by a
special health visitor. An agreed percentage of children will be