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Following the outbreak, the Director of the Colindale Laboratory offered
sufficient gamma globulin for the immunisation of 177 children attending the school.
The offer was made to the parents of all the children except those in classes
taking the Grammar School Entrance Examination and the parents of 344 children
accepted. A random sample of 177 was selected and each child was immunised with
1½ c c. of gamma globulin on 3rd February, 1956 11 was explained that the immunity
was not likely to last more than six weeks
The progress of the epidemic was followed carefully and during the next three
months only three further cases occurred in unimmunised children
Date of onset
J.S. 20. 2. 56. who was not offered immunisation
as he was in a class taking the
examination.
D. A. 27. 2. 56. whose parents had not given consent for immunisation*
S.C. 29.2.56.
The investigation of this outbreak is informative in two respects. First, the
onset of a large number of cases during the middle two weeks of January suggests
that the two children marked * who were absent from school seven days and eleven
days respectively may have been infectious when they returned to school in mid
December.
A second interesting aspect of the investigation is that only three cases
occurred in the school after the immunisation;, although only one third of the total
had been immunised, and therefore approximately 300 children were not immune
It is postulated that by increasing the degree of herd immunity in a school so
that one third are immune, the school ceases to be a favourable nidus for the continuation
of the epidemic
I am indebted to the Area Medical Officer of the Middlesex County Council for
the assistance given to me in carrying out these inoculations and investigations,
NOTIFICATION
The disease is not notifiable As the incubation period is usually about twentyeight
days the epidemics are spread over a long period and the effect on school
absences is seldom serious at any one time
Cases which show jaundice are easily diagnosed but diagnosis is more difficult
when jaundice is absent Such cases are equally responsible for the spread of
infection and for this reason it is probable that the disease has not been made
notifiable.
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