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| Journal of the New Zealand Medical Association,
13-March-2009, Vol 122 No 1291
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|
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.
MethodsDe-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
ResultsBecause 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.
DiscussionStudy
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: bjloring@yahoo.com
References:
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