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73
Measles.
The year 1937 was not an epidemic one in Acton, and in
only one school was there any interference with school work from
measles.
Since the end of the Great War, Measles has regularly
appeared in the district in epidemic form in alternate years, and
these have been the even years—1936, 1934, 1932, etc. Sporadic
cases always occur in a district like ours, which is not a self-contained
area. So much immigration and emigration occur, that
isolated cases are always cropping up, but when an isolated case
occurs in an interepidemic year, there has been very little danger
at spread of the disease even in the Infants' departments. The
theory is held, and events seem to prove its correctness, that during
an epidemic the community is immunised either by a clinical attack
or by a subclinical infection. A clinical attack usually confers a
belong immunity, and a sub-clinical infection confers immunity
which may extend to a couple of years or more. An epidemic dies
down when the herd immunity reaches a certain level. In the past
quarter of a century, the conditions have favoured the occurrence
of an epidemic every two years.
Circumstances can arise, such as immigration, reduction in
the Size of families, etc., which would alter the epidemiological
course of the disease, as the history of Measles in the district shows.
When the district was rapidly developing, the epidemiology
of the disease was different, and a regular biennial visitation was
the exception and not the rule.
A small outbreak in West Acton Infants' School last summer
an interesting from an epidemiological standpoint, because the
course of events was probably influenced by immigration and the
tendency towards reduction in the size of families.
This school was opened in February 1937, and although the
from which its pupils are recruited is now almost entirely built
constitutes that part of the district most recently developed,
immigration has relatively been more extensive here than in
the rest of the district; moreover, the families are smaller in size.
some cases of Measles occurred in the district in the summer,
but it was only in the West Acton School that it spread. Over 30
cases occurred here in the summer term, but only isolated cases
occurred in the other Infants' departments. Most of the children
who suffered were either in one-child families, or were the eldest
children in the family, conditions which would make it likely that