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A distinguishing feature of the autumn epidemic was the relatively higher fatality among children
under 5 years of age, chiefly at ages between 2-5 years. The deaths in Chicago, New York, Rome, and
other cities, also show in varying degree a high incidence at these ages. There is a suggestion
in the figures for the nine metropolitan boroughs for which particulars have been received that the
deaths among children under five years of age are relatively highest in the poorest populations.
This also appears clearly in the figures for the Dublin registration area. The maximum mortality in
London in the autumn prevalence was reached somewhat earlier in the epidemic at those ages in
which the total of deaths was highest than at other ages.
The age-incidence of influenza mortality in 1918 offers a remarkable contrast to that
usually seen in earlier epidemics. The characteristic of influenza mortality has hitherto been a
high incidence in infancy and old age. There was observable in the epidemic of 1890, the first of any
importance after that of 1847-8, a relatively higher incidence at ages 20-45, than in 1847-8 or in the
succeeding years 1891 and 1892; indeed, there is a progressive decline in the relative mortality at these
ages in 1891 and 1892 upon that of 1890, and a corresponding increase in incidence at higher ages.
In 1893, however, the age-inciderce reverts to that of 1890; and from a comparison of the changes
of age-incidence in the six years 1890-1895 the only definite conclusion to be drawn is that the greater
the number of deaths the smaller the proportion at ages 20-45. With this rule the 1918 deaths are,
however, directly at variance. Nor is it easy to frame any theory of immunity acquired in the
epidemics of 1890-95 which will fully account for the abnormal age-incidence of 1918.
Nevertheless the effects of immunization (and possibly also of sensitization) cannot be altogether
set aside. The interval between the present pandemic and that which commenced in 1890 is
shorter by 15 or 20 years than the interval between 1890 and the next preceding pandemic; hence while
people aged between 20 and 40 who suffered in the "forties" of the last century would not have survived
as a rule until 1890, the people between 20 and 40 who were attacked in the "nineties" of the last
century would still be alive in many cases in 1918.
Thus on the one hand, if it be assumed that sufferers from repeated attacks, in years about the
time of a pandemic prevalence, acquire an immunity which protects them at the time of a later
pandemic, this would serve to explain the comparatively light mortality at the higher ages in the
recent prevalence.
On the other hand, if it be assumed that sufferers in one pandemic prevalence are more liable
to attack in later pandemics, the hypothesis would explain how it is that children who suffered markedly
in 1890, having grown to ages 25-35 in 1918, again suffered in excess.
It may be, however, that there is a difference in age-incidence of mortality in epidemic as compared
with endemic and sporadic cases of influenza, analogous to that observed between epidemic
cerebrospinal meningitis and sporadic cases of this disease. If that be regarded as a sufficient
explanation the extent to which either form of disease is predominant might be held to determine the
age-incidence of mortality in any particular year.
It has been suggested that the congregation of large numbers of the population of ages between
20-45 in munition works and in camps, may account for the excessive mortality at this age period.
While this factor must undoubtedly be taken into account, so far as the mortality at these ages is corcerned,
it does not explain the high incidence of death upon children, especially upon those between
2 and 5 years of age. If, however, it could be assumed that a severer type of disease had been predominant
among men on service, it might be urged that the civil population with which they come into most
intimate association would be their wives, whose ages would average between 20 and 35, and their
children of ages mainly between 2 and 15 years.
Again, the ages of special incidence, 2-5 and 25-35 are perhaps more affected by restrictions of diet
than other ages ; children from 2-5 because of their rapid growth, and particularly their rapid muscular
development; ages 25-35 because these are the ages of hard physical labour in the civil population,
and, it should be added, this labour has been largely done by the more or less unfit owing to the depletion
in war time of the physically fit population ; among articles of diet the reduction of which would have
lessened resistance to disease at these ages that of animal fat is probably the most important.
Sir Richard Redmayne, Chief Inspector of Mines, in the course of his evidence before the Coal Mines
Commission on the 11th March last, stated that so severe were the effects among miners of the epidemic
of influenza that in many collieries as many as 50 per cent, of the workers were absent day after day.
The mortality in many of the small towns central to mining areas is found to be altogether excessive
compared with non-industrial towns of the same size in the autumn.
Dr. King Brown, Medical Officer of Health of Bermondsey, in reporting upon the course of the
epidemics in that borough, mentions that no cases occurred in the consumptive wards of the infirmary;
should this experience prove to be general, light may be thrown on the conditions affecting the incidence
of the disease.
Consideration has been limited above to the age-incidence of deaths certified as due to influenza.
It is, however, evident from the figures given, that many deaths during the course of the epidemic
which were certified to be due to bronchitis, pneumonia, phthisis, heart disease, etc., either directly
resulted from an attack of influenza or were hastened thereby. Undoubtedly a proportion of these cases
would have terminated fatally, independently of the epidemic, but were the number of such instances
considerable, there would have been a reaction, after the epidemic had passed, resulting in a decline in
the proportion of deaths from these particular causes, since the number of persons suffering fatally
from them would have become temporarily reduced below the normal. Of such a reduction there is,
however, little or no evidence in the figures.
The effect of the epidemic upon the age-incidence of these causes of death is considerable, but as
the ages most affected are those of highest influenza mortality the figures given above, relative to the age-
Anomalous
age incidence
of
1918.