Journal of the New Zealand Medical Association, 13-March-2009, Vol 122 No 1291
Routine vaccination coverage of 11 year olds, by ethnicity, through school-based vaccination in South Auckland
Belinda J Loring, Elana T Curtis
New Zealand’s National Immunisation Schedule (NIS) currently includes a diphtheria, tetanus, and pertussis booster (dTap) at age 11.1 There are no published vaccination coverage rates for this age group in New Zealand, and data on this age-group will not be available from the National Immunisation Register until the birth cohort reach age 11 in 2016.
New Zealand’s coverage of other childhood vaccinations has historically been poor, and inequalities in coverage between Māori and non-Māori have been documented in all immunisation surveys to date.1 Understanding vaccination uptake in the adolescent age group is important as it is the target age-group for the new human papillomavirus (HPV) vaccine. The purpose of this analysis is to evaluate coverage data for the routine 11-year-old (Year 7) vaccinations, using data from Counties Manakau District Health Board’s (CMDHB) school-based vaccination programme.
De-identified aggregate data were obtained with permission from the CMDHB Public Health Nurses (PHN) Database on the 11-year-old tetanus and polio vaccinations from 2005. These were the routine vaccinations recommended by the NIS for all 11 year olds at the time, and were given as single dose, separate vaccinations. The 2005 year was chosen as it was the most recent year with all data entry complete.
Aggregate numbers, by ethnicity were extracted, for the following categories:
The data were analysed, using standard descriptive statistical methods in STATA v9.1 software, to determine percentages of form return, consent and vaccination receipt by ethnicity, including relative risks for Māori compared to non-Māori students.
Because vaccinations were carried out throughout the academic year, the Year 7 (Form 1) school category was used rather than a specific age range. The PHNs relied on teachers to distribute consent forms to students, and only collected data from those forms returned. The PHN database did not contain the total number of Year 7 students on the school rolls, so the total number of Year 7 students in these schools, by ethnicity, was obtained from the Ministry of Education (from the July 2005 roll return).
More students were classified as “Other” in the PHN database than through the Ministry of Education’s system of ethnicity classification. This discrepancy suggests limitations in the reliability of ethnicity classification, which will be explored further in the discussion. The “Other” category is not analysed on its own in the following analyses, but is included along with the other ethnicities to make up the category “non-Māori”.
The Ministry of Education data comes from the self-identified ethnicity recorded by parents on the school enrolment form. The PHN database is populated from the CMDHB PiMS database, which is the patient record database used by the whole CMDHB. For approximately 95% of students, the ethnicity extracted from the PHN database will reflect the ethnicities given at the time of their first admission to hospital or involvement with CMDHB rather than the ethnicities they nominated on the Year 7 vaccination consent form.2
For both databases, a student is recorded in one ethnic group only, even though they may list up to three ethnicities on both the school enrolment and vaccination consent forms. The Ministry of Education uses the system of ethnicity priority recommended by Statistics New Zealand which prioritises Māori, then Pacific, Asian, and Other ethnicities if more than one ethnicity is selected. The PHN database also prioritises only one ethnicity, with the primary ethnicity being the patient’s “main ethnicity” as determined by the patient or the data-entry clerk at time of entry onto the CMDHB PiMs system.3,4
Because there were no significant differences between the results for the tetanus and the polio vaccinations, only the results for the tetanus vaccination will be discussed in this article.
Table 1 shows the form return, consent and vaccination rates for each ethnic category (as total student numbers and simple percentages) for the tetanus vaccination.
Out of all students on the Year 7 school roll for 2005, only 54% received tetanus vaccination through the school-based programme. This result is influenced by findings showing 25% of parents declined consent for vaccination in school and another 13% did not return a consent form at all. This picture varied greatly by ethnicity—Māori had much higher rates of not returning a form (36%), compared with NZ European (3%), but of the forms returned, NZ European had higher rates of refusing consent (37%) than Māori (18%).
A total of 24% of Year 7 (28% of those who returned forms) did not consent to have tetanus in school. School vaccination coverage varied by ethnicity, with Pacific having the highest coverage (59%), followed by Asian (51%). There was no significant difference between the school coverage rates for Māori (48%) and New Zealand (NZ) European (49%). Higher coverage was achieved for Pacific than for Māori, partly because the form return rate was higher for Pacific and a higher percentage of Pacific students actually received vaccination once consented, despite a higher proportion of Māori consenting to vaccination on the forms that were returned.
1Values >100% due to discrepancy in ethnicity classification between numerator and denominator—this is further clarified in methods and discussion; *Mostly of Samoan, Tongan, Niuean, or Cook Islands origin.
Table 2 compares the form return, consent and vaccination rates of Māori with non-Māori. This table includes relative risks for Māori compared to non-Māori of returning a consent form, consenting to vaccination in school, and actually receiving vaccination in school. Only 64% of Māori on the Year 7 school roll returned vaccination consent forms, compared to 94% for non-Māori overall (RR=0.68, 95%CI 0.66–0.71).
Coverage rates for Māori were lower than non-Māori. For Māori, 48% in Year 7 were vaccinated in school. For non-Māori, 56% received the tetanus vaccination in school. Out of those who did return forms, Māori were significantly more likely than non-Māori to consent to school vaccination (RR=1.18, 95%CI 1.14–1.21).
Even though once consented, Māori were more likely than non-Māori to actually receive vaccination (RR=1.06, 95%CI 1.04–1.09), this did not overcome the effect of non-return of forms and left Māori significantly less likely than non-Māori to receive tetanus vaccination through the school based programme (RR=0.85, 95%CI 0.81–0.90).
1Statistically significant values are in bold; *All are p=0.0000
Table 3 compares the reasons given for non-consent between Māori and non-Māori, including relative risks. Major explanations include the child already being immunised (50%) or parents intending to have the child immunised by GP (24%).
Data entry in this category in the PHN database is likely to be incomplete, as only 15 non-consenters were entered as having “no option selected”, leaving a large number (n=392) of non-consenters remaining unaccounted for in these figures. There was no statistically significant difference between the number of Māori and non-Māori who did not consent because they did not agree with vaccination (8% of those declining consent), nor between the number not consenting because they preferred to take their child to the GP.
Māori were 22% less likely than non-Māori (RR=0.78 95% CI 0.66-0.93) to decline consent because their child had already been immunised.
Table 3. Comparison of reasons given for non-consent to Year 7 vaccination 2005, between Māori and non-Māori
1 Statistically significant values are in bold.
Fifty percent of parents declined consent for school vaccination because they stated their child had already received the vaccinations. If we assume that this self-reported vaccination status is correct, this increases the coverage of the scheduled 11-year-old vaccination in this population to 67% overall, 53% for Māori, and 71% for non-Māori. If we expand this estimate to include all parents who stated their child had already received and those who were planning to receive their tetanus vaccination in primary care, this provides an optimistic upper estimate of coverage in this population of 55% for Māori and 78% for non-Māori. In both these estimates, coverage increases more for non-Māori than Māori.
Study limitations—The absence of school roll data in the PHN database made it difficult to accurately assess form return and vaccination rates. Vaccination was undertaken throughout the school year, and the Ministry of Education denominator refers to a snap-shot of the school rolls during July 2005, so it is possible that there was some minor fluctuation in school roll numbers throughout the year, especially in the South Auckland setting. It is, however, assumed that there would have been minimal net change in student numbers.
The results are limited by a discrepancy in the ethnicity classification between the CMDHB PHN data and the Ministry of Education datasets. Ethnicity numerator/denominator bias may be present because of three main factors: differences in the “Other” category, differences in the source of ethnicity data, and differences in the prioritisation of multiple ethnicities. More students were classified as “Other” in the PHN database (n=643) compared with the Ministry of Education data (n=368). If these “Other” students in the PHN database are disproportionately made up of one particular ethnic category, the effect will be to under-represent the form return and vaccination coverage of that ethnicity. It is likely, however, that the excess “others” are made up of a mixture of Māori and non-Māori, as the relative vaccination coverage for each ethnic group found in this analysis is consistent with ethnic trends in coverage found in similar analyses, such as the MeNZB™ programme,5 with Pacific receiving the highest coverage followed by Asian, NZ European, and Māori.
These difficulties illustrate the ongoing problem of inadequate ethnicity data collection for Māori in New Zealand. This is despite evidence highlighting the problem of under-counting in health statistics for Māori6–8 and the creation of clear ethnicity data protocols for the health and disability sector.9 The fact that this problem remains within vaccination data is concerning, as it prevents Māori inequalities from being fully identified, understood, and addressed.
General discussion—In New Zealand, even where a school-based vaccination programme is in place, scheduled vaccinations may still be given in primary care. This makes it difficult to be certain about the overall vaccination coverage in this population.
This analysis found that out of the 30% of parents who declined school vaccination, half had already vaccinated their children (presumably in primary care), and another quarter intended to vaccinate their child in primary care. This information is less reliable for Māori, as we only have information on the 11% of Māori parents who declined consent, and have no information on the vaccination status or preferences of the 36% of Māori who did not return a form.
There are also well-documented problems10,11 associated with the accuracy of self-reported vaccination status, and in this analysis the status of children reported to have been vaccinated or due to be vaccinated in primary care is unable to be verified. This type of analysis would have been greatly assisted if these children had been entered on the NIR, which would have enabled confirmation of vaccinations reported as given in primary care.
Out of those refusing consent, Māori were significantly less likely to have been immunised in primary care, suggesting access barriers to primary care or preferences against using this setting, and adding further weight to the hypothesis that school-based vaccination delivery works better for Māori.
These data provide the only estimate of coverage for the 11-year-old scheduled vaccination in New Zealand. Using data from a DHB which had a high proportion of Māori enabled roughly similar sample sizes for each ethnic group, meaning close to equivalent explanatory power for Māori. As a result, all relative risks calculated for Māori compared with non-Māori were statistically significant.
This analysis only refers to one DHB, and this DHB may not be representative of the rest of New Zealand. To gain a more balanced and representative understanding of vaccination delivery to 11 year olds in New Zealand, and for a fuller assessment of Māori:non-Māori inequalities, similar analyses of coverage would need to be undertaken in rural settings and primary care, particularly in the South Island where school-based delivery is not used.
The most striking finding for Māori in this analysis was the large percentage who did not return a consent form. We have no information about the reasons for this, and do not know what proportion of these parents would have liked their child vaccinated and how many had been, or were, intending to be vaccinated elsewhere.
We know from other attitudinal studies that Māori parents do not have significantly different views on vaccinations,12–15 so it is highly unlikely that these Māori who did not return consent forms were all objectors to immunisation.
A number of factors, such as higher school mobility, illness, and absenteeism rates might explain some of this disparity in form return rates for Māori students, but it is likely that other factors also contribute. Process factors, such as how consent forms were actually distributed to students, the nature and style of the consent form, and the timeframes involved are all potential areas to explore in order to understand and improve this system for Māori.
It is encouraging that once consented, Māori were more likely than non-Māori to receive vaccinations, but with such a large percentage of Māori not returning forms it is difficult to draw strong conclusions from this, and the opposite was found in the MeNZB™ programme with Māori less likely to receive vaccinations once consented.5
The results of this study suggest that a mixed delivery system, using both schools and primary care, works less well for Māori than non-Māori. Whilst overall coverage in this population increased when including those who had or intended to be vaccinated in primary care, the disparity in coverage between Māori and non-Māori also increased. This indicates that primary care is a less commonly accessed setting for this immunisation for Māori compared with non-Māori, and that more equitable outcomes for Māori might be achieved by concentrating on improving the school based vaccination delivery. This is supported by findings from the MeNZB™ programme, where school based delivery achieved less disparity in coverage between Māori and non-Māori compared to delivery in primary care.5
Conclusion—Coverage for the Year 7 tetanus vaccination in this population in 2005 was low overall, and was much lower for Māori. Overall, 48% of Māori and 56% of non-Māori in Year 7 in CMDHB in 2005 were immunised through the school-based programme. Assuming that parents who stated their child had already received these vaccinations were all correct, the overall coverage in this population for the recommended Year 7 tetanus and polio vaccination is 53% for Māori and 71% for non-Māori.
The coverage of the year 7 vaccination was limited by the fact that a quarter of parents refused consent and another one-eighth did not respond by returning a consent form. Coverage for Māori was limited mostly by the fact that over a third did not return a consent form, and further research is needed into reasons and solutions for this.
Once consented, Māori were slightly more likely than non-Māori to actually receive their vaccinations. This evidence is limited by different methods of ethnicity data collection, and is limited to one DHB only. Further coverage assessments need to be undertaken in different settings, such as rural areas, and areas where immunisation are delivered in primary care.
Competing interests: None known.
Author information: Belinda J Loring, Public Health Medicine Registrar, Waitemata District Health Board, Takapuna, Auckland; Elana T Curtis, Public Health Physician, Senior Lecturer Medical, Te Kupenga Hauora Māori, Faculty of Medical and Health Sciences, University of Auckland
Acknowledgements: Belinda Loring received financial assistance as a trainee with the Australasian Faculty of Public Health Medicine (AFPHM) whilst undertaking this project. We also thank Nettie Knetsch, Sue Miller, and Natalie Dawson from CMDHB for assistance with the data, and the Immunisation Advisory Centre for general advice.
Correspondence: Dr Belinda Loring, Waitemata District Health Board, Private Bag 93-503, Takapuna, Auckland, New Zealand. Email: firstname.lastname@example.org
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