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It will thus be noted that whilst the desirability of offering to the community
the advantages of this method of protection against diphtheria is becoming increasingly
recognised by the metropolitan borough councils and, although the numbers
of persons actually dealt with are growing, the dilution of the total child population
by so small a number of actively immunised persons, as shown in the above table,
can exert but little effect upon the incidence of diphtheria as a whole. As has already
been pointed out, schemes of active immunisation must depend for their success upon
the amount and character of the efforts expended upon propaganda. In this connection
it must be realised that education of the parents cannot be otherwise than a
gradual process. Unfortunately parents do not realise the seriousness of diphtheria
until an outbreak of the disease occurs among the susceptible community. Active
immunity by means of toxoid anti-toxin, however, takes too long to become established
for the necessary protection to be afforded in the presence of an outbreak,
but when once it is established the effect is said to be lasting, at any rate sufficiently
long to cover the period of school life, i.e., at the ages when the disease is most
dangerous to life.
The only method of conferring rapid or prompt protection upon persons who
have been exposed to infection is by means of passive immunisation, i.e., the administration
of small doses of anti-toxin, the protective effect of which is only of
three weeks' duration. This method, whilst practicable and commonly used in
residential institutions, is not applicable to day schools. The Council is prepared to
place at the disposal of metropolitan borough councils where immunisation schemes
have been adopted, facilities for using the school organisation in the distribution of
propaganda leaflets prepared by the borough medical officers, subject to their approval
by the Education Committee. Up to the present applications by eight borough
medical officers for the use of such facilities have been received and granted.
Judging from the experience in this country in districts, or in institutions,
where immunisation schemes have been in force for a sufficient length of time,
this method of prevention of diphtheria appears to afford an effective protection
in all but a very small proportion of cases. Dr. O'Brien, Director of the Wellcome
Research Laboratories, recently pointed out that the results of investigation carried
out in those laboratories showed that 95 per cent. of persons immunised, when retested
after 7 years, were still immune as demonstrated by negative reactions to the Schick
test. Similarly, it was shown that, in 98 per cent. of persons Schick tested, a negative
reaction persisted over such a period of time as to suggest that it was a lasting
condition. In a certain small number of instances cases of diphtheria have been
reported among those who have received the requisite three immunising doses, but
in such cases, on closer investigation, it has been found that the person was not
suffering from true diphtheria but from tonsilitis or some other condition simulating
diphtheria, that the period required for completion of the immunising process had
not elapsed, or that the person had not been retested after the requisite lapse of
time to determine lasting immunity.
Very few instances have come to light of immunised persons contracting
diphtheria after the full immunising course and after retesting, and judging from
available records such cases are usually mild in character. Similarly, to explain
the somewhat rare occasions on which a Schick negative reactor has been found
to be suffering from diphtheria, it has been suggested that there may be certain
individuals whose amount of natural anti-toxin is on the border line, subject to slight
fluctuations and not constantly stable, according to the extent and frequency of
exposure to mild doses of infection on which the normal individual is probably dependent
for maintaining natural immunity. The exposure of such an individual to a
massive dose of infection may possibly result in an attack of diphtheria developing
when the natural anti-toxin is temporarily reduced. These anomalies, however,
occur but rarely, and so add to the difficulty of investigation and explanation.