Discussion

Efficacy of history taking as a screening method for detecting incomplete immunisation relies on two factors: first, that the question is asked, and second, that the information given by parents is accurate.

Our data show that approximately three-quarters of children were asked about their immunisation status. The question was less likely to be asked for non-medical presenting complaints and with increasing age of the child. In our ED, only medical presentations are seen by paediatricians and this may explain why an immunisation history is taken less frequently with other presentations. Older children may be asked less frequently because it is perceived as less relevant, or there may be the confounding factor that they are more likely to present with non-medical complaints.

When an immunisation history was taken, there was a low sensitivity for detecting incomplete immunisation. Fewer than half of those who were in fact overdue correctly identified themselves as such. Of those who reported that they were incomplete, over half were insufficiently overdue to meet our criteria, and PCT records showed that the majority did receive their outstanding immunisations shortly following their PED presentation. The negative predictive value of 95.8% means that approximately 1 in 20 patients reported as up to date were in fact overdue, which has important implications for ED or out-of-hours clinicians assessing unwell children by highlighting that the possibility of a vaccine-preventable disease should not be completely excluded from the differential diagnosis by an up-to-date immunisation history. In our sample population, immunisation coverage was 93.1% (95% CI 90.9% to 94.9%). This is slightly lower than the coverage for our PCT region of 95.7% (estimate from published immunisation coverage by 5 years)5 and may reflect a reduced uptake in children who attend PED.

The strengths of our study include the large number of notes surveyed, although, because of the low prevalence of being overdue, our CI for sensitivity is still relatively wide. Using a retrospective review of medical notes, it is possible that discussions occurred about immunisation status but were not documented. We have no record of the way in which the question about immunisations was asked, and it is possible that the method of asking led to incorrect responses rather than inaccurate knowledge on the part of the parent. Studies in Australia in relation to the Australian Childhood Immunisation Register found that for those identified as overdue on the register, immunisation history was incorrect in the notes for more than half of these children.6 This and other studies also found from surveys of parents that between 40% and 85% of children showing as overdue on the register were actually fully immunised.7 ,8 However, we believe that there are important differences between the Australian and UK health systems, particularly that in the UK all residents have an NHS number which enables transfer of health records with them when they move location, which should improve the accuracy of records and mean they are suitable for use as a reference standard. In our study, PCT staff also checked with the original data from GP practices for children identified as overdue. However, it is possible nonetheless that some of the children who we classified as overdue were in fact completely immunised, and if this were the case, the estimated sensitivity would be somewhat higher.

There are several reasons which may account for the poor sensitivity of history taking. The parent may simply have forgotten that the immunisations are incomplete or the question may be asked in insufficient detail to correctly ascertain if there are omissions from the schedule. For some children, parents may know that their child is overdue but not wish to open a discussion about this with health professionals. Sensitivity of screening through history was lower for older children, and this may be related to a reduced parental focus on child health as children get older.

The combination of incomplete coverage of questioning about immunisation and low sensitivity of screening by history resulted in identification of only about a third of children with incomplete immunisation. This is a missed opportunity for opportunistic immunisation or discussion about the importance of vaccination. Previous studies have demonstrated the importance of health professionals in determining parental attitudes towards immunisation9 and that opportunistic immunisation would be taken up if offered.3

While coverage of immunisation history taking could be improved, for example, by making it a required part of admission or discharge documentation, this alone is unlikely to significantly improve detection of those overdue because of the low sensitivity of the history. Our study shows that older children with minor injuries are less likely to be asked, and so education to clinicians or modifications to the clerking proforma, to target this group may be particularly beneficial. An ideal strategy for improving detection could instead focus on alternative tools to assess immunisation status of PED attendees, such as linking the PCT database to the PED system, so a child who is overdue can be flagged up on arrival and steps taken to rectify this while they are in hospital. However, the cost implication of this is likely to outweigh the benefit in the population studied, where overall coverage is quite high and the number of children who could be offered opportunistic immunisation relatively small. Future research could involve parent interviews to better assess the relationship between medical history, parental knowledge of immunisations, and the PCT database. In the interim, highlighting the cohort of patients who present as fully immunised, but may actually be incomplete for immunisations, may be helpful to clinicians.