A History of Epidemics in Britain, Volume 2 (of 2) / From the Extinction of Plague to the Present Time - Charles Creighton

Percentage of
smallpox deaths
above five years

Percentage of
measles deaths
above five years

Percentage of
scarlatina deaths
above five years

	Smallpox	Measles	Scarlatina
Total at all ages	909	2318	1085
Under One year	209	353	88
One to Two	133	832	167
Two to Three	91	511	181
Three to Four	81	272	183
Four to Five	63	153	115
Five to Ten	136	168	254
Ten to Fifteen	33	18	46
Fifteen to Twenty	34	3	14
Twenty to Twenty-five	54	1	8
Twenty-five to Thirty	38	2	6
Above Thirty	37	5	23

The ratio of smallpox deaths above five was 37·5 per cent., of measles deaths 8·4 per cent., and of scarlatina deaths 32·3 per cent. Measles and scarlatina have kept these ratios somewhat uniformly to the present time, but the ratio of smallpox deaths above the age of five has increased according to the following table for England and Wales from 1851 to 1890:

The progressive raising of the age of fatal smallpox is shown in another way by taking the ratio of the deaths per million living at all ages and at each of eleven age-periods[1177]:

Smallpox Deaths per million living at each age-period.

Period	All ages	0-	5-	10-	15-	20-	25-	-35	-45	-55	-65	75 and over
1851-60	221	1034	257	73	93	130	92	53	38	24	18	14
1861-70	163	654	145	56	86	136	102	73	49	36	26	22
1871-80	236	527	284	137	197	300	239	168	111	71	46	35

It was the great epidemic of 1871-72 that brought out the change of age-incidence most concretely, just as it brought out, in contrast to the last great epidemic in 1837-40, the decline in the rural and the increase in the industrial centres. In the three years before the outburst of 1871 the deaths under five and over five were approaching an equality; in the epidemic itself the old ratios were suddenly reversed:

Year	Smallpox deaths under five	Smallpox deaths over five
1868	1234	818
1869	892	673
1870	1245	1375
1871	7770	15356
1872	5758	13336

In the whole generation between 1840 and 1871, in which there was no great and general epidemic of smallpox, many had passed from childhood to adolescence and maturity without encountering the risk of it. When the epidemic of 1871 began, it found many in youth or mature years who had not been through the smallpox, and it attacked a certain proportion of them accordingly. The proportion above the age of five so attacked in 1871-72 was greater than it had been in this country since the beginning of the 18th century; indeed, as the information is not in statistical form for the earlier period, it may be asserted, and it may happen to be true, that it was greater than it had ever been in this country at any time. The reason for the large proportion of adult cases was the same in the rise of smallpox as in its decline, namely, that in the respective circumstances an epidemic found many who had not been through the disease in infancy or childhood. The same happened in those parts of the world where the epidemics of smallpox came at long intervals, during which many had passed from childhood to youth or mature age without once encountering the risk of smallpox.

Such were the epidemics at Boston, New England, and Charleston, South Carolina, in the 18th century. Not only do the accounts of them speak of the disease as if it were mainly one of the higher ages, but it follows from the ratio of attacks to population, known in the case of Boston, that adolescence and adult age must have had a full share, considering that these age-periods included all who were protected by a previous attack. The years of epidemic smallpox at Boston were 1702, 1721, 1730 and 1752: of these four the two worst were 1721 and 1752, the one epidemic following a clear interval of nineteen years, the other a more or less clear interval of twenty-two years: