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is probably due to the temporary influence of protection derived from natural
maternal immunity. Such immunity is gradually lost, as evidenced by the increasing
number of children between the ages of 6 months and 5 years found to be Schick
positive.
Later, as the result probably of exposure from time to time to mild doses of
diphtheria infection, the individual acquires some degree of immunity, reflected in
the reduced number of those found to be Schick positive and in the lower incidence
of diphtheria and case mortality after the age of 6 years.
Confirmation of these facts, mainly established in America, has been provided
by the results obtained by workers both in this country and in France, though
restricted to a limited number of investigations during the past three years.*
Zingher, in 1921, from application of the test to 52,000 children drawn from every
class of life in New York, found considerable variation in the immunity rate of town
and country dwellers, poor and well to do. In the poorer town quarters the percentage
of Schick negative (immune) school children proved to be as high as 80.84;
in good class schools only 33, and in a rural school but 15 per cent were found immune,
a range dependent on the degree to which the various groups of individuals had been
exposed to infection and had acquired a corresponding passive immunity. The
prophylactic use of diphtheria toxin-antitoxin injection under the skin for the
purpose of actively immunising the non-immune or Schick positive school child,
first proposed by Von Behring in 1913, has been carried out on a very considerable
scale by American workers in the past two years. In view of the very high proportion
of children between the ages of 6 months and 6 years found to be Schick positive,
and therefore unprotected, Zingher has considered it advisable in future to dispense
with the preliminary test, and particularly in time of epidemic, and to immunise all
children from 5 months up to the age of 6, reserving the test only for adults and children
over 6 years.
The method of immunisation now practised in America consists in the subcutaneous
injection of three doses of toxin-antitoxin mixture, each of 1.25 c.c. and
given at intervals of two weeks.
After completion of the series, certificates of immunity are only given when
immunity is proved by subsequent negative reaction to the Schick test—a varying
period which may not be reached for two or three months. Those proving still
Schick positive receive a second, or, it may be, a third series of injections before
complete immunity is established. Quite exceptionally cases occur which persistently
remain Schick positive after one or more series of injections.
Park (New York) states (Journal American Medical Association, May, 1922);
We have seen no harmful effects from the application of the Schick test and the use
of toxin-antitoxin in more than 100,000 school children. At a later date (January,
1923) he has recorded (in the New York State Journal of Medicine) the fact that
the New York department of health had 180,000 children indexed and under observation,
of whom 90,000 have been Schick tested. Of this number, 60,000 have
proved negative at the original test, 30,000 received toxin-antitoxin injections
and of these 20,000 were negative when re-tested subsequently. 10,000 of those
originally positive had either not been re-tested or on re-test were still found positive
after the injections.
Results of
active
immunisation.
*An interesting addition to the literature on the Schick test has recently been published
by the Medical Research Council in their Special Report Series, No. 75, this being a report by
Surgeon-Commander Sheldon F. Dudley, R.N., on throat illness in a London school. It is
deserving of note that in this report comparison is made between about 1,000 boarders and
100 day boys in the school. Diphtheria, scarlet fever, and sore throat affected 30 per cent, of
the former, but no single case of diphtheria or scarlet fever was reported among the day boys.
Taking a broad view of the facts it seems likely that the boarders of the school, recruited as
they are from all parts of the country, come to the London environment without the protection
which previous school life here might have afforded. With regard to the day boys,
most of them are undoubtedly Londoners, who may have been protected by previous attack.