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IO6
of immediate attack below one-twentieth, vaccination 20 to 30 years before
reduced it below one-twelfth, vaccination 30 to 40 years before reduced it to
one-ninth, and if more than 40 years before to less than one-half. For statistical
purposes "protection" after vaccination may be regarded as adequate for
30 years, though it is no longer at its maximum potency after 20 years.
Amongst persons vaccinated within 5 years about .1 in 150 may be expected to
contract variola minor when exposed to infection in the house. It is estimated
that in this epidemic prior vaccination saved 332 and subsequent vaccination
saved 135 home contacts from attack, leaving out of account the persons infected
by these cases.
11. The mean number of persons living per dwelling was higher in houses
invaded by small-pox than for the Borough as a whole. The proportion of
contacts unprotected did not show any relation to the number of persons in the
house. The attack-rate amongst the unprotected contacts increased in general
with the number of persons living in the house, but was definitely lower in
households of 10-12 persons than in households of 4-6, this being no doubt due
to separation into two or more families occupying different rooms. Although
no evidence is found that a protection rate as high as 00% suffices to protect a
community from the spread of an epidemic, as distinct from protecting the
vaccinated persons in it, the risk to unvaccinated persons in an infected house
appears to have been considerably reduced when more than half the persons
living in the house were protected by vaccination, the important factor being
the ratio of protected to unprotected persons rather than the actual numbers of
each.
The following is a summary of the work done by the Vaccination Officers
with regard to Small Pox : —
Whitechapel
and Mile End.
Limehouse
and St. Georges.
Visits to premises where cases of Small Pox
have occurred
10
17
Visits to Seamen's Lodging Houses
—
2
Visits to firms affected
3
6
V isits to schools affected
3
2
No. of contact notices served
220
196