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76
that this is markedly true of the great improvement
in Diphtheria mortality which has occurred during the
past 34 years. Whether such improvements would
be enhanced by immunisation is arguable. The
difficulty is that if there is some long term biological
cycle which influences these statistics, in addition to
such factors as current economic circumstances and
their effect upon the resistance to disease, one cannot
very well distinguish between what has been the
result of the natural curve, the environmental factor
or the active immunisation measures. In the absence
of substantial proof of this kind, is it the proper line
of action to launch a vigorous immunisation campaign
(anything less would appear to be of little value) or
to appropriate the money and labour involved towards
other more tangible public health activities ?
In considering a possible national drive for
Diphtheria immunisation, if this be the proper course,
it is well to bear in mind that unless 60 to 70 per cent,
of the child population is immunised the aim of a
protected community cannot be realised. At present,
we know that a large number of children are so-called
Diphtheria carriers (I say " so-called " because they
are usually not carrying virulent Diphtheria bacilli)
and consequently as children enter school they probably
receive infinitesimal doses of infection, thereby obtaining
a certain degree of herd immunity. This is
indicated by work that has been done in the East End
in testing children as to their susceptibility to
Diphtheria, from which it would seem that 60 to 70
per cent, are insusceptible, thus leaving us with about
30-40% susceptibles. When one adds to this analysis
the difficulties experienced relative to vaccination, it
is questionable whether the response to voluntary
immunisation would be sufficient to produce any
more appreciable effect in a district like Bethnal Green.
In all the circumstances, the weight of evidence
seems to me to be decidedly in favour of the second
of the two courses indicated above.