Group Title: BMC Public Health
Title: Support for immunization registries among parents of vaccinated and unvaccinated school-aged children: a case control study
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Title: Support for immunization registries among parents of vaccinated and unvaccinated school-aged children: a case control study
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Language: English
Creator: Linkins, Robert
Salmon, Daniel
Omer, Saad
Pan, William
Stokley, Shannon
Halsey, Neal
Publisher: BMC Public Health
Publication Date: 2006
 Notes
Abstract: BACKGROUND:Immunizations have reduced childhood vaccine preventable disease incidence by 98–100%. Continued vaccine preventable disease control depends on high immunization coverage. Immunization registries help ensure high coverage by recording childhood immunizations administered, generating reminders when immunizations are due, calculating immunization coverage and identifying pockets needing immunization services, and improving vaccine safety by reducing over-immunization and providing data for post-licensure vaccine safety studies. Despite substantial resources directed towards registry development in the U.S., only 48% of children were enrolled in a registry in 2004. Parental attitudes likely impact child participation. Consequently, the purpose of this study was to assess the attitudes of parents of vaccinated and unvaccinated school-aged children regarding: support for immunization registries; laws authorizing registries and mandating provider reporting; opt-in versus opt-out registry participation; and financial worth and responsibility of registry development and implementation.METHODS:A case control study of parents of 815 children exempt from school vaccination requirements and 1630 fully vaccinated children was conducted. Children were recruited from 112 elementary schools in Colorado, Massachusetts, Missouri, and Washington. Surveys administered to the parents, asked about views on registries and perceived utility and safety of vaccines. Parental views were summarized and logistic regression models compared differences between parents of exempt and vaccinated children.RESULTS:Surveys were completed by 56.1% of respondents. Fewer than 10% of parents were aware of immunization registries in their communities. Among parents aware of registries, exempt children were more likely to be enrolled (65.0%) than vaccinated children (26.5%) (p value = 0.01). A substantial proportion of parents of exempt children support immunization registries, particularly if registries offer choice for participation. Few parents of vaccinated (6.8%) and exempt children (6.7%) were aware of laws authorizing immunization registries. Support for laws authorizing registries and requiring health care providers to report to registries was more common among parents of vaccinated than exempt children. Most parents believed that the government, vaccine companies or insurance companies should pay for registries.CONCLUSION:Parental support for registries was relatively high. Parental support for immunization registries may increase with greater parental awareness of the risks of vaccine preventable diseases and utility of vaccination.
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Research article


Support for immunization registries among parents of vaccinated
and unvaccinated school-aged children: a case control study
Robert W Linkins', Daniel A Salmon*2,3, Saad B Omer3, William KY Pan3,
Shannon Stokley4 and Neal A Halsey3


Address: 'Thailand Ministry of Public Health US CDC Collaboration, National Center For HIV, STD, and TB Prevention (previously at National
Immunization Program), Centers for Disease Control and Prevention, Atlanta Georgia 30333, USA, 2Department of Epidemiology and Health
Policy Research, College of Medicine, University of Florida, 1329 SW 16th Street, Room 5239, Gainesville, Florida 32608, USA, 3Department of
International Health, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room W5041, Baltimore, Maryland 21205, USA
and 4National Immunization Program, Centers for Disease Control and Prevention, Mailstop E-05, 1600 Clifton Rd., NE, Atlanta, Georgia 30333,
USA
Email: Robert W Linkins robertl@tuc.or.th; Daniel A Salmon* das@ehpr.ufl.edu; Saad B Omer somer@jhsph.edu;
William KY Pan wpan@jhsph.edu; Shannon Stokley ZMA2@cdc.gov; Neal A Halsey nhalsey@jhsph.edu
* Corresponding author



Published: 22 September 2006 Received: 21 March 2006
BMC Public Health 2006, 6:236 doi: 10.1 186/1471-2458-6-236 Accepted: 22 September 2006
This article is available from: http://www.biomedcentral.com/1471-2458/6/236
2006 Linkins et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.



Abstract
Background: Immunizations have reduced childhood vaccine preventable disease incidence by 98-100%. Continued
vaccine preventable disease control depends on high immunization coverage. Immunization registries help ensure high
coverage by recording childhood immunizations administered, generating reminders when immunizations are due,
calculating immunization coverage and identifying pockets needing immunization services, and improving vaccine safety
by reducing over-immunization and providing data for post-licensure vaccine safety studies. Despite substantial resources
directed towards registry development in the U.S., only 48% of children were enrolled in a registry in 2004. Parental
attitudes likely impact child participation. Consequently, the purpose of this study was to assess the attitudes of parents
of vaccinated and unvaccinated school-aged children regarding: support for immunization registries; laws authorizing
registries and mandating provider reporting; opt-in versus opt-out registry participation; and financial worth and
responsibility of registry development and implementation.
Methods: A case control study of parents of 815 children exempt from school vaccination requirements and 1630 fully
vaccinated children was conducted. Children were recruited from 112 elementary schools in Colorado, Massachusetts,
Missouri, and Washington. Surveys administered to the parents, asked about views on registries and perceived utility and
safety of vaccines. Parental views were summarized and logistic regression models compared differences between
parents of exempt and vaccinated children.
Results: Surveys were completed by 56.1% of respondents. Fewer than 10% of parents were aware of immunization
registries in their communities. Among parents aware of registries, exempt children were more likely to be enrolled
(65.0%) than vaccinated children (26.5%) (p value = 0.01). A substantial proportion of parents of exempt children support
immunization registries, particularly if registries offer choice for participation. Few parents of vaccinated (6.8%) and
exempt children (6.7%) were aware of laws authorizing immunization registries. Support for laws authorizing registries
and requiring health care providers to report to registries was more common among parents of vaccinated than exempt
children. Most parents believed that the government, vaccine companies or insurance companies should pay for
registries.



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Conclusion: Parental support for registries was relatively high. Parental support for immunization registries may
increase with greater parental awareness of the risks of vaccine preventable diseases and utility of vaccination.


Background
Immunizations have been tremendously successful in the
United States, reducing childhood vaccine preventable
diseases (VPDs) by 98-100% [1,2]. However, this impres-
sive accomplishment does not guarantee future success:
immunization coverage must be maintained to avoid
resurgence of disease [3]. The immunization schedule has
become increasingly complex as new vaccines have been
introduced, making it difficult for parents and health care
providers to remember the immunization schedule and
comply with vaccine recommendations.

Immunization registries can help ensure high immuniza-
tion coverage. As defined by the National Vaccine Advi-
sory Committee (NVAC), immunization registries are
"confidential, computerized information systems that
contain information about immunizations and children"
[4]. Immunization registries can be used for measuring
vaccine coverage, generating reminders when immuniza-
tions are due and recalls when immunizations are over-
due, identifying pockets of need for targeted
interventions, improving vaccine safety by reducing over-
immunization and calculating accurate denominators
important for post-licensure vaccine safety studies, as well
as many other important public health functions [4]. The
federal government, states and non-profit organizations
such as the Robert Wood Johnson Foundation's All Kids
Count Program have invested substantial resources into
the development of immunization registries, yet only
48% of U.S. children less than 6 years old are enrolled in
a registry [5]. Only 76% of public and 39% of private vac-
cination provider sites reported administered immuniza-
tions to a registry in the last six months of 2004 [5].
Immunization registries must be fully operational and
contain complete immunization records in order for their
potential to be wholly realized.

Parental support for immunization registries has not been
well characterized. Focus group research indicates that,
although most parents are very positive about registries,
they tend to follow their doctors' advice regarding partici-
pation [4]. The NVAC [4] and the Centers for Disease
Control and Prevention [6] recommend that parents be
given a choice about participating in immunization regis-
tries. The decision to participate can be "opt-out" (the reg-
istry is automatically populated using birth registry or
other means and parents can choose to have all or part of
their child's information removed) or "opt-in" (requires
parental permission before any information about the
child is entered into the registry). Opt-out registries are


generally more efficient as it is easier to enter information
at birth and then give parents the choice to remove the
data rather than depending on an active response by par-
ents.

Many states have laws to assist in the establishment and
implementation of registries. As of October 2000, 24 of
51 jurisdictions (50 states and District of Columbia) had
legislation authorizing the establishment of a registry, 12
mandated provider reporting to the registry, and 14
required explicit consent (opt-in) to be in a registry [8].
Parental support for these types of state registry laws has
not been explored. Understanding parental support for
immunization registries is important to registry develop-
ment, as registries require substantial public funding and
extremely high parental participation for their potential to
be realized.

Much debate has surrounded who should pay for immu-
nization registries [4]. Registry development, to date, has
been financially supported by federal, state and local
funding, private foundations, and managed care organiza-
tions [7]. During NVAC discussions, it was suggested that
those who benefit from immunization registries should
contribute to the cost of registry development and main-
tenance, including health care providers, vaccine compa-
nies and parents/patients [4].

The objectives of this study were: (1) to characterize sup-
port for immunization registries and laws authorizing reg-
istries and requiring providers to report to registries, and
(2) to characterize parental preference for registry partici-
pation (opt-in and opt-out) and determine who they
believe should pay for registries among parents of vacci-
nated and unvaccinated school-aged children.

Methods
We conducted a case-control study of the parents of 815
children (cases) who were exempt (for any reason, includ-
ing medical) for one or more vaccine antigens required by
law for school entry and the parents of 1630 fully vacci-
nated children (controls). Two vaccinated control chil-
dren in the same grade and school were randomly selected
per case child. Children were recruited from 112 private
and public elementary schools (grades kindergarten
through 5) in Colorado (n = 25), Massachusetts (n = 23),
Missouri (n = 34), and Washington (n = 30). Twenty
exempt children were identified as siblings with different
last names when the school addressed the envelopes and
older siblings were removed from the study to avoid send-


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ing a duplicate survey to the same household. Study selec-
tion and recruitment methods have been described in
detail elsewhere [9]. The states were selected based on the
proportion of exemptions (low, medium and high com-
pared with other states) and geographical distribution of
states. Immunization registry attributes were not a consid-
eration for state selection as the primary study purpose
was to explore immunization exemption issues. This
study was approved by the Committee on Human
Research, Johns Hopkins Bloomberg School of Public
Health.

Survey content
Parents of exempt children were asked to verify that their
child had not received one or more vaccines required for
school entry and if the child received the complete or less-
than-complete number of doses for each vaccine series.
Parents who indicated that they did not have their child
vaccinated for medical reasons were asked to indicate the
medical condition that contraindicated vaccination.
Respondents were provided with a brief description of
immunization registries and asked to indicate if they sup-
port or oppose registries on a five point Likert scale rang-
ing from "strongly oppose" to "strongly support"; if they
were aware of a registry in their area and, if so, if their
child was enrolled in the registry; and if they were aware
of and if they would support laws authorizing immuniza-
tion registries and requirements for health care providers
to report to registries. Respondents were given a brief
description of "opt-in" and "opt-out" and asked to indi-
cate their preference to these options and whether having
a choice regarding participation affected their support for
registries. Respondents were informed that it costs about
$4 per child per year to have an immunization registry
[7,10], and were asked if they thought this was a good use
of money and, if so, who should pay for immunization
registries (parents, doctors, insurance companies, govern-
ment, other, or not sure). Respondents were also asked to
use a five point Likert scale to estimate the probability that
an unimmunized child would contract a disease for which
vaccines are recommended for elementary school chil-
dren (polio, measles, mumps, rubella, diphtheria, pertus-
sis, tetanus, haemophilus influenzae type b, hepatitis B, and
varicella) during a ten year period ("impossible" to "very
likely"); how serious it would be for an 8-year-old to
develop one of these diseases ("not at all serious" to "very
serious"); how effective the vaccines are in preventing
children from getting these childhood diseases ("not at all
protective" to "very protective"); and how safe the vaccine
is ("dangerous" to "very safe"). Respondents were asked
to self identify demographic characteristics, including age
(9 categories, starting with 18-20 years and continuing by
5-year intervals with > 61 as the highest), education (6 cat-
egories of grade completed: grade 4, grade 8, grade 12 or
GED test, some college, college graduate, or postgraduate,


and race or ethnicity (White, Hispanic, Black non-His-
panic, Native American, and other). Surveys took approx-
imately 30 minutes to complete; a sample is available on-
line [11].

Data analysis
Parents were excluded from the primary data analysis if
their child had been listed by the school as exempt but the
parent indicated that their child was fully vaccinated, or if
the parent provided a medical contraindication compati-
ble with ACIP/AAP guidelines (based on review by the
senior author).

Support for registries, laws authorizing registries, and laws
requiring providers to report to registries were dichot-
omized into "strongly support" or "support" versus all
other responses. Frequency of survey responses were cal-
culated by state and were tested for differences in propor-
tion answering each question affirmatively using the
Fishers Exact Test. Frequency of survey responses were cal-
culated for parents of vaccinated children and parents of
exempt children. Odds ratios were used to compare differ-
ences in responses between parents of exempt (any anti-
gen) and vaccinated children. In order to assess if survey
responses (outcome variables) varied among parents of
exempt children by the number of antigens a child was
exempt for, exempt children were further categorized into
4 groups: exempt for 1 antigen, exempt for 2-5 antigens,
exempt for 6-9 antigens and exempt for 10 antigens. The
Cochran-Armitage test for trend was conducted across vac-
cinated children and children exempt for different num-
bers of antigens (vaccinated children and 4 groups
described above) [12,13].

General constructs for respondents' assessments of disease
susceptibility and severity, and vaccine efficacy and safety
were created using the respondent's mean scores for all 10
antigens/diseases. These construct scores were dichot-
omized by the lower quartile among all respondents, indi-
cating if a parent had "low" perceived disease
susceptibility and severity and vaccine efficacy and safety.
A logistic regression model was used to assess support for
immunization registries (outcome variable) associated
with low disease susceptibility and severity and low vac-
cine safety and efficacy (independent variables), adjusting
for the vaccination status of the child (exempt versus vac-
cinated). Relationships between independent and
dependent variables were generally consistent across
states (data not presented) and consequently state data
were combined.

Results
Surveys were returned by 391(48.6%) of the 805 parents
of exempt children and 976 (59.9%) of the 1630 parents
of fully vaccinated children, for an overall response rate of


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56.1%. Information on non-responders was not collected
and consequently it is not possible to compare responders
to non-responders.

Of the 391 parents of exempt children identified by the
school, 86 reported that their children were fully vacci-
nated and an additional 28 provided valid medical con-
traindications for vaccination. These 114 children were
dropped from the analysis. The remaining 277 parents of
children with non-medical exemptions were included in
the analyses; 33 (11.9%) children were exempt for 1 anti-
gen, 73 (26.4%) children were exempt for 2-5 antigens,
57 (20.6%) children were exempt for 6-9 antigens, and
114 (41.1%) children were exempt for all 10 antigens.

The median age of respondents was 36-40 years and par-
ents of exempt children tended to be a bit older than par-
ents of vaccinated children. The median level of education
for the study sample was some college, and parents of
exempt children tended to be a bit more educated. The
majority of vaccinated respondents (91.7%) and exempt
respondents (94.5%) were white. The majority of surveys
(88.5%) were completed by mothers.

Registry characteristics of the study states are summarized
in Table 1. Fewer than 10% of parents were aware of
immunization registries in their communities (Table 2),
with a state range of 4.0% (Massachusetts the only opt-
in state) to 11.7% (Missouri). Respondents in Missouri
and Washington were more likely to report being aware of
a law authorizing an immunization registry compared
with Colorado and Massachusetts (Table 2). Among par-
ents aware of registries, exempt children were more likely
to be enrolled in an immunization registry (65.0%) than
vaccinated (26.5%) children (p value = 0.01). Few parents


of vaccinated or exempt children were aware of laws
authorizing immunization registries (6.8% and 6.7%,
respectively). Support for laws authorizing registries and
requiring health care providers to report to registries was
more common among parents of vaccinated than exempt
children, although parents with children exempt for only
one antigen expressed similar support as parents of vacci-
nated children (Table 3). Support for registries, support
for law authorizing registries, and support for law requir-
ing providers to report to registries (Table 3) decreased
with increasing numbers of exemptions, a statistically sig-
nificant trend.

Parents of vaccinated children were more likely to support
opt-out compared with opt-in registries and parents of
exempt children were more likely to support opt-in com-
pared with opt-out registries (Table 4). A statistically sig-
nificant trend was identified among parents of exempt
children for preference toward opt-in, preference toward
opt-out, support for registries regardless of choice, and no
support for registries despite choice. Providing a choice
for participation in registries increased parental support
among parents of exempt children, from 32.6% (Table 3)
to 45.4% (Table 4), yet the availability of choice had little
impact on support for registries among parents of vacci-
nated children. The majority of parents of vaccinated chil-
dren (70.7%) and a substantial proportion of exempt
parents (45.4%) supported immunization registries either
because of or regardless of choice regarding registry partic-
ipation (Table 4). Only 7.5% of parents ofvaccinated chil-
dren did not support registries despite choice, while more
than 20% of parents of vaccinated children were unsure of
their support for registries ("don't know"). Parents of vac-
cinated children were more likely than parents of exempt
children to report that registries are worth $4 per year per


Table I: Immunization Registry characteristics of Colorado, Massachusetts, Missouri and Washington


Registry Characteristic [19]

Catchment area
Provisions for participation
Populated by birth data?
Child participation level a
% of public providers enrolled in registry
% of enrolled public providers submitting data within past 6 months
% of private providers enrolled in registry
% of enrolled private providers submitting data within past 6 months

Registry Legislation [20]
State law authorizing immunization registry
State law mandate reporting?
Type of consent needed to enter the registry
If implied consent, are there provisions to opt out or limit access to the
registry?


Colorado Massachusetts Missouri


Regional
Opt-out
Yes
43%
89%
62%
30%
57%


Regional
Opt-in
No
7%
84%
67%
3%
100%


Yes No
No N/A
Implied consent Written consent
No N/A


Statewide
Opt-out
Yes
81%
100%
78%
22%
38%


Washington

Statewide
Opt-out
Yes
76%
86%
99%
44%
98%


No No
N/A N/A
Implied consent Implied consent
No Yes


a Child participation level is defined as the proportion of children less than 6 years of age in the catchment area who are enrolled in the registry with
2 or more immunizations recorded.


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Table 2: Frequency (Percent) of Parents who are Aware of and Support Immunization Registries (IRs) by State

Colorado Massachusetts Missouri Washington Total Fishers Exact Testa P Value


Aware of IR
If Aware of IR, Child Enrolled in IR
Support IR
Aware of Law Authorizing IR
Support Law Authorizing IR
Support Law Requiring Providers to Report to
IR


a = Fishers Exact Test is a chi square test that computes exact p values with no approximation.


child (Table 5). Most parents believed that the govern-
ment, vaccine companies or insurance companies should
pay for registries as opposed to parents (Table 5). Support
for immunization registries was lower among parents
with low perceived disease susceptibility (Odds Ratio
(OR): 0.56; 95% Confidence Interval (CI) 0.39-0.81),
disease severity (OR: 0.49; 95% CI 0.35-0.68), vaccine
safety (OR: 0.51; 95% CI 0.36-0.74), and vaccine efficacy
(OR: 0.63; 95% CI 0.44 0.91), adjusting for the child's
vaccination status.

Discussion
Most parents were not aware of immunization registries,
including parents in Missouri and Washington, states that
report greater than 75% of children are enrolled in regis-
tries. Parental support for registries was relatively high,
particularly among parents of vaccinated children and
parents of children with an exemption to only one anti-
gen. A substantial proportion of parents of exempt chil-
dren supported immunization registries, particularly if
registries offered choice for participation, notable given
that these parents refused one or more vaccines recom-
mended for children. We were surprised to find that par-
ents aware of registries were more likely to have their child


enrolled in a registry if the child was exempt rather than
vaccinated. Nearly a third of parents of vaccinated and
exempt children did not indicate a preference for opt-in
versus opt-out, suggesting that this difference may not be
important to many parents.

The increased support for registries among parents of
exempt children when participation is optional suggests
that this may be an important registry attribute in gaining
support for vaccine registries among parents who do not
fully vaccinate their children. Yet, parental support for
immunization registries may not be a strong predictor in
registry participation given our study found that few par-
ents were aware of registries even in states with high regis-
try participation and most parents (even parents with
antigen-specific exemptions) support registries. Greater
efforts may be needed to make parents aware of registries
to ensure that parents are properly informed. Anecdotal
information suggests that only a small proportion of par-
ents choose to opt-out or refuse to opt-in to immuniza-
tion registries [7]. Our study findings suggest that opt-out
may be a preferred strategy to opt-in given overall parental
support for registries and the general efficiency of opt-in
versus opt-out.


Table 3: Frequency (Percent) of Parents Aware and Supportive of Immunization Registries (IRs) by Child's Vaccination Status


Vaccinated Exempt for Any
Antigens


Unadjusted Odds
Ratio and 95% Cla,b


Number of Antigens Exempt For


I 2-5 6-9 10


Aware of IR
If Aware of IR, Child Enrolled in IR
Support IR
Aware of Law Authorizing IR
Support Law Authorizing IR
Support Law Requiring Providers to
Report to I R


66 (7.8)
9 (26.5)
652 (71.7)
66 (6.8)
51 I1 (81.6)
494 (78.3)


18 (7.6)
8 (65.0)
80 (32.6)
18 (6.7)
49 (32.0)
55 (35.3)


0.96 (0.56-1.66)
5.14 (1.68-15.71)
0.19 (0.14-0.26)
0.98 (0.57-1.67)
0.1 1 (0.07-0.16)
0.15 (0.10-0.22)


a: Odds Ratio compares parents of children exempt to any antigens to parents of vaccinated children. Interpretation of odd ratios: Parents of
exempt children who were aware of registries had about 5 times as high odds of having their child enrolled in a registry compared with parents of
vaccinated children who were aware of registries.
b: Odds Ratio in Bold P-Value < 0.05
* Trend test is statistically significant at <0.05


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19 (5.6)
6 (31.3)
232 (67.0)
17 (4.9)
244 (70.2)
241 (69.5)


14 (4.0)
7 (50.0)
212 (60.6)
12 (3.4)
241 (68.7)
237 (67.7)


28 (11.7)
9 (32.1)
151 (63.3)
24(10.2)
174 (73.0)
165 (69.2)


34 (1 1.5)
15 (45.0)
189 (63.7)
30(10.0)
230 (77.7)
218 (73.5)


95 (7.7)
37 (38.2)
784 (63.7)
83 (6.5)
889 (72.2)
861 (70.0)


I (3.8)
0 (0.0)
21 (75.0)
1 (3.2)
11 (84.6)
8 (72.7)


7(10.4)
3 (42.9)
26 (40.6)
7 (9.6)
20 (46.5)
19(44.2)


4 (8.5)
2 (66.7)
SI (22.0)
4 (7.3)
6 (18.2)
11 (28.9)


6 (6.1)
4 (75.0)
20 (20.6)*
6 (5.4)
12 (18.8)*
17 (26.6)*


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Table 4: Frequency (Percent) of Parental Preference for Opt-In vs. Opt-Out and Immunization Registry (IRs) Support by Child's
Vaccination Status


Vaccinated Exempt for Any
Antigens


Unadjusted
Odds Ratio and
95% Cla,b


Number of Antigens Exempt For


2-5 6-9


Prefer Opt-Inc
Prefer Opt-Outd
Don't Know
Total
Support IR regardless of choice
Support IR because of choice
Do not support IR
Don't Know
Total


(32.7)
342 (36.0)
297(31.3)
950 (100.0%)
334 (34.7)
347 (36.0)
72 (7.5)
210 (21.8)
963 (100.0%)


133 (50.0)
54 (20.3)
79 (29.7)
266 (100.0%)
25 (9.3)
97(36.1)
76 (28.3)
71 (26.3)
269 (100.0%)


2.06 (1.55-2.71)
0.45 (0.33-0.63)
0.93 (0.69-1.25)


0.18 (0.12-
1.00 (0.76-
4.87 (3.41-
1.29 (0.95-


a: Odds Ratio compares parents of children exempt for any antigens to parents of vaccinated children. Interpretation of odd ratio: Parents of
exempt children had about 3 times as high odds of preferring opt-in compared with parents of vaccinated children.
b: Odds Ratio in Bold P-Value < 0.05
* Trend test is statistically significant at <0.05
c: "opt-in" requires parental permission before any information about the child is entered into the registry
d: "opt-out" registry is automatically populated using birth registry or other means and parents can then have all or part of their child's information
removed


This study has the potential for non-response bias. If bias
exists, the likely result is an overestimate of support for
registries as parents who do not recognize the value of vac-
cines and immunization registries may have been less
likely to complete vaccine related surveys. It is also possi-
ble that parents opposed to immunization registries were
more motivated to respond. We were unable to compare
child or parental characteristics between participants who
completed surveys and those who refused, since no infor-
mation was collected on refusals and the investigators
were blinded to the names of respondents. Participation
in immunization registries, registry types and registry laws
vary by state and such differences may account for some
of the differences in study finding by state. While the
maturity of state registries and registry characteristics were


not included in state selection criteria, the four states
included in this study represent a rather broad range of
registries (Table 1). Few parents were aware of registries
which limits the generalizability of our findings. Parental
reporting of enrollment may suffer from information bias
as parents may have had their children enrolled in regis-
tries but were not aware of this. Schools were not selected
based upon registry catchment area and consequently it
was not possible to link parental responses with access to
immunization registries. Care should be taken in general-
izing from this study to the entire nation; parents were
selected from only four states.

Associations found between support for immunization
registries and perception of susceptibility to and severity


Table 5: Frequency (Percent) of Parental Beliefs regarding Financial Worth and Responsibility of Immunization Registries (IRs), by
Child's Vaccination Status


Is IR worth $4/Child/Year

Yes
No, Opposed to IR
No, Cost Too Much
Don't Know
Total
Who Should Pay for IR a
Government
Vaccine Companies
Insurance Companies
Parents
Don't Know
Doctors

a: Not Mutually Exclusive


Page 6 of 8
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11 (35.5)
10(32.2)
10(32.3)
31 (100.0%)
9 (30.0)
13 (43.3)
2 (6.7)
6 (20.0)
30(100.0%)


32 (44.4)
19(26.4)
21 (29.2)
72(100.0%)
8 (11.3)
33 (46.5)
16 (22.5)
14 (19.7)
71 (100.0%)


35 (63.6)
6 (10.9)
14 (25.5)
55 (100.0%)
3 (5.3)
22 (38.6)
20 (35.1)
12 (21.0)
57(100.0%)


55 (50.9)*
19 (17.6)*
34 (31.5)
108 (100.0%)
5 (4.5)*
29(26.1)
38 (34.2)*
39 (35.2)*
I I I (100.0%)


Vaccinated

450 (47.1)
73 (7.6)
108 (I 1.3)
325 (34.0)
956 (100.0%)

302 (30.9)
245 (25.1)
21 I1 (21.6)
153 (15.7)
89 (9.1)
68 (7.0)


Exempt

41 (15.3)
87 (32.5)
33 (12.2)
107 (40.0)
268 (100.0%)

40(14.4)
49(17.7)
21 (7.6)
15 (5.4)
26 (9.4)
6 (2.2)


P-Value

<0.01
<0.01
0.65
0.07


<0.01
0.01
<0.01
<0.01
0.89
0.01


BMC Public Health 2006, 6:236








http://www.biomedcentral.com/1471-2458/6/236


of VPDs, and safety and efficacy of vaccines, suggest that
parental support for immunization registries may increase
with greater parental awareness of the risks of VPDs and
utility of vaccination. For diseases that have been effec-
tively controlled, many parents are not aware of the risks
of disease [14].

Health care providers play an important role in parents'
decision making about vaccine issues[ 15]; provider atti-
tudes toward immunization registries likely affect paren-
tal attitudes toward immunization registries. Support for
immunization registries by health care providers is critical
for their success and many parents may rely on health care
providers for determining participation in registries. In a
recent study, the need to consolidate scattered vaccine
records, closely followed by state mandated participation,
was identified as the most influential reasons for provider
registry participation [16]. Reasons for not participating in
registries including too much resources, duplicate sys-
tems, lack of awareness of registry, incompatibility with
existing data systems, confidentiality concerns, few pedi-
atric patients, and insufficient technical support [16]. Pro-
vider participation in registries has been shown to vary by
type of provider (pediatrician, family physician, nurse),
type of provider practice (private practice, HMO, public or
community clinic), size of practice, and community type
(urban/rural) [17,18].

Conclusion
Parents of vaccinated and unvaccinated school-aged chil-
dren in the four states surveyed were largely unaware of
the immunization registries in their region or state, even
with reported child participation rates ranging from 7% to
81%. Despite this lack of awareness, the majority of par-
ents interviewed were supportive of immunization regis-
tries, legislation authorizing immunization registries, and
laws mandating provider reporting to registries. However,
parents of exempt children were less like to be supportive
of registries and registry legislation, and this lack of sup-
port increased as the number of vaccines their children
were exempted for increased. Nonetheless, a substantial
proportion of parents of exempt children supported
immunization registries, particularly if registries offer
choice for participation.

The usefulness of immunization registries correlates with
the proportion of the childhood population enrolled as
well as the quality of immunization data contained in the
registry. Without high participation rates, targeted immu-
nization interventions to areas of low immunization cov-
erage will be of little value. Without complete and
accurate immunization records, providers will under-
standably have little faith in registry information and
ignore registry attributes of providing immunization deci-
sion support and generating messages to alert parents that


their children are due or delinquent for a vaccine. With an
increasingly complex immunization schedule, these
attributes are becoming essential strategic elements to
maintaining high immunization coverage levels.

Competing interests
The authors) declare that they have no competing inter-
ests.

Authors' contributions
RL contributed to data analysis and interpretation, and
manuscript development. DS contributed to study design,
survey instrument development, data analysis and inter-
pretation, and manuscript development. SO contributed
to study design, data collection and analysis, and manu-
script development. WP contributed to data analysis and
interpretation, and manuscript development. SS contrib-
uted to study design and data interpretation. NH contrib-
uted to study design, survey instrument development,
data analysis and interpretation, and manuscript develop-
ment. All authors read and approved the final manuscript.

Acknowledgements
This study was funded by a grant from CDC.

The findings and conclusions in this report are those of the authors and do
not necessarily represent the views of the Centers for Disease Control and
Prevention/the Agency for Toxic Substances and Disease Registry.

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