II. THE INCIDENCE OF IMMUNISATION IN DIFFERENT GROUPS

It was explained in the introduction how a sample of children aged under sixteen was selected from the National Register, and the mothers of these children interviewed. Before the subject of immunisation was broached by the interviewer, mothers were asked two questions “Do you know what causes diphtheria?” and “Do you know how diphtheria can be prevented?”, with the purpose of measuring the extent of their knowledge. Before dealing with the replies to these questions it is however useful to establish the proportions of children immunised in different sections of the population, as these proportion form the essential background against which the results of the first two questions, and of the other questions asked, can be evaluated.

Questions about immunisation were asked of mothers with reference to the particular child selected from the Register, and the proportions of children immunised given in this section are based upon the information collected about this sample of children. However, mothers were also asked how many children they had, and whether the other children in the family had been immunised, for the purposes of establishing the proportions of mothers who had had none, some or all of their children immunised, and for making analyses of answers given to the questions designed to test mothers’ knowledge about diphtheria.

Interviewers were told to record children as being immunised if they had already been given one injection. A separate question was asked as to whether the immunisation had been completed by a second injection, and the results of this question are dealt with later on. However, it may be said here that in 95% of cases, immunisation had been completed. Children, whose mothers had agreed to having them immunised, but who were at the time of interview still waiting to have their first injection, were not counted as being immunised.

Altogether 2,584 interviews were made. Of the children selected, 67% had been immunised and 33% had not. Allowing for the sampling error it may be said that something between 65% and 69% of all children under sixteen in England and Wales, have been immunised (i.e. received at least one injection).

This would amount to a little over six million children. It was estimated that 5,334,206 children had been immunised in 1944. Some of these would have reached the age of sixteen since being immunised. In dealing with these results, it was thought best to express the number immunised as a percentage of all the children considered, although of course some babies who would not yet have reached a suitable age for immunisation are included in the total. However, in dealing with the proportion of mothers who had had one or more of their children immunised, mothers who had only small babies, who had not yet reached their first birthday, were excluded, since it might be expected that about three quarters of these babies would not be old enough to be immunised.

4% of all the mothers interviewed had only babies aged less than one. Of the remainder, those with one or more children who had passed their first birthday, 81% had had one or more of these children immunised, and 19% had not had any of them immunised. The 81% comprises 65% having every child (or the only child) aged one or over immunised, and 16% who had both immunised children, and children who had not been immunised.

It is of some interest to note that of all the children of all the mothers interviewed, 5,797 in all, 68% had been immunised, a figure which agrees closely with the 67% given by the selected sample.