Transcript Measuring Immunization Coverage among Pre

Measuring Immunization Coverage
among Pre-School Children:
Past, Present and Future Opportunities
Presented by
Daniel A. Salmon, PhD, MPH
Department of Epidemiology and Health Policy Research, College of Medicine,
University of Florida, Gainesville, Florida
Institute for Vaccine Safety & Department of International Health, Johns Hopkins
Bloomberg School of Public Health, Baltimore, Maryland
Why I Love to Work with Vaccines
Vaccines can be one of the most effective
public health tools – prevention at its
greatest! Those who work in vaccines are
very lucky to be able to help prevent
horrible diseases from hurting children.
We have the potential to save lives and
even, on rare occasions, to try to eradicate
disease. It’s very exciting!
This presentation is based on information from the
following article:
Salmon DA, Smith PJ, Navar AM, Pan WK,
Omer SB, Singleton JA, Halsey NA. Measuring
Immunization Coverage among Preschool
Children: Past, Present, and Future
Opportunities. Epidemiologic Reviews. 2006;
28:27-40
Background
• Vaccines are very important! 1,2
• Control of vaccine-preventable diseases
depends on maintenance of high
immunization coverage
• Coverage among preschool children remains
suboptimal
Rationale for Measuring Immunization
Coverage among Preschoolers
1. Ensure young children protected from
vaccine-preventable diseases
2. Ensure rapid and equitable uptake of new
vaccines
Indicators for Immunization
Measurement among Preschoolers
1. Age-appropriate vaccination status
2. Up-to-date vaccination status 3
Measuring Immunization Coverage
among Preschoolers
• Parental recall of vaccination often
inaccurate4
• Age at measurement varies
Immunization Measurement among
Preschoolers
• Local measurement useful
– Pockets of low-coverage susceptible to
5
outbreaks
– Special interventions needed to improve
local coverage
Measuring Immunization
Coverage:
State and Local Methods
Retrospective School Surveys: Methods
1. Public and [sometimes] private schools
sampled
2. School immunization records examined
3. Algorithms created to retrospectively
measure coverage at different ages
4. Records compared with National
Immunization Survey
Retrospective School Surveys: Strengths
• Capitalize on existing infrastructure
• High completion rates
• Include children who have migrated into
study area
6
Retrospective School Surveys: Weaknesses
• School record completeness variable
• Parental completion of immunization
history may be inaccurate
• Miss children who migrate out of study
area prior to school entry
• Miss homeschooled children in some
states
• Timeliness of data
Retrospective School Surveys: Attributes
Interval from age 24 months until
survey results:
Standardization between states/study
populations?
Within state/study population
measures of coverage?
Proportion of children with completed
immunization information:
Antigens included:
Quality control?
Labor intensiveness:
2-5 Years
Potentially
Yes, if population based
98% (all but homeschooled children,
assuming complete school records)
Usually only antigens required for
school entry, but can include all
Needs to be explored
Modestly labor intensive – utilizes
existing infrastructure
Includes children who migrate into
area?
Yes
Includes children who migrate out of
area?
No
Birth Certificate Follow-back Surveys:
Methods
1. Children born during specified time
period randomly selected using birth
certificates
2. Children located
3. Immunization histories collected
Birth Certificate Follow-back Surveys:
Strengths
• Initial birth cohort well defined
• Comparatively short interval between data
collection and survey results
• All recommended antigens potentially
included
Birth Certificate Follow-back Surveys:
Weaknesses
• Extremely resource intensive
• Miss children immigrating into study area
after birth
• Low completion rates create potential for
bias
• Validity questionable if immunization
histories not verified
Birth Certificate Follow-back Surveys: Attributes
Interval from age 24 months until
survey results:
Standardization between states/study
populations?
Within state/study population
measures of coverage?
Proportion of children with completed
immunization information:
Antigens included:
Quality control?
Labor intensiveness:
Includes children who migrate into
area?
Includes children who migrate out of
area?
Variable – usually 1-2 years
Potentially
No
Variable
All recommended by
ACIP/AAP/AAFP
Variable
Extremely labor intensive
No
Potentially – adds significantly to cost
Household Cluster Surveys: Methods 7
1. Regions divided into non-overlapping
clusters
2. Clusters sampled
3. Households contacted until sufficient
number identified within each cluster
4. Obtain immunization histories of
children in household.
Household Cluster Surveys: Strengths
• Efficient
• Coverage estimates valid for individual
clusters
• Coverage can be compared from one
region to another
Household Cluster Surveys: Weaknesses
• Costly in rural areas
• Validity questionable if immunization
histories not verified
• Methodology prone to bias
Household Cluster Surveys: Attributes
Interval from age 24 months until
survey results:
Variable – usually 1-2 years
Standardization between states/study
populations?
Potentially
Within state/study population
measures of coverage?
Potentially
Proportion of children with completed
immunization information:
Antigens included:
Quality control?
Labor intensiveness:
Variable
All recommended by
ACIP/AAP/AAFP
Variable
Labor intensive – particularly in
rural areas
Includes children who migrate into
area?
Yes
Includes children who migrate out of
area?
Yes
Measuring Immunization
Coverage:
National Surveys
History of National Immunization
Coverage Measurement
• 1957: Census Bureau adds questions regarding
polio vaccine to the Current Population Survey 8
– Termed “United States Immunization Survey”
• First national immunization survey in U.S.
• 1957-1970: conducted via household interviews
• 1970-1985: conducted over the telephone
• Discontinued in 1985
• Unable to generate sub national coverage estimates 6
• Limited validity due to respondent recall 9
History of National Immunization
Coverage Measurement
• CDC begins passively monitoring vaccine
uptake8,10, 11
1. Vaccine manufacturer reports
2. Biologics Surveillance System
History of National Immunization
Coverage Measurement
• CDC conducted retrospective school surveys
– Found association between lower immunization
rates and increased measles incidence in
12
preschoolers in 1980’s
History of National Immunization
Coverage Measurement
• National Health Interview Survey (NHIS)
begins collecting vaccination coverage
information
• National Immunization Provider Record
Check Study verifies household coverage
reports
• 2004: Immunization information removed
from NHIS
The National Immunization Survey:
• Children 19-35 months living in U.S.
households
• Coverage estimates give up-to-date rates
of doses of seven vaccines 14
• Coverage estimates published by CDC
annually
National Immunization Survey
• In addition to vaccine coverage rates, survey
examines associated issues, such as
– Breastfeeding 15, 16
– Participation in WIC program 17
– Impact of child-care on immunization status 18, 19
– Associations between physician distribution and
immunization rates 20
– Type of health care utilized for vaccination 21
– Number of provider visits 22, 23
– Impact of invalid vaccine doses 24, 25, and
– Vaccine safety beliefs 17, 26
National Immunization Survey
• Survey results assist in
– Determining national vaccine needs
– Determining level of state funding
National Immunization Survey: Methods
•
•
Quarterly surveys conducted in 78
Immunization Action Plan areas
Phases of data collection
1. List-assisted, random-digit dialing survey
2. National Immunization Survey Provider
Record Check survey
National Immunization Survey: Strengths
• Standardized coverage estimates allow for
state comparisons
• Survey infrastructure
• Timeliness
National Immunization Survey (NIS) Composite
Response Rate, 1995-2003
100
80
60
40
20
0
1995
1996
1997
1998
1999
2000
2001
Composite Response Rate
2002
2003
National Immunization Survey Response Rates, 1995–2004
In 2004, the product of these three proportions was 32.0% 29
Comparisons of Vaccine Coverage Estimates
Reference
Rosenthal (30)
Seattle (31)
Bastis (32)
HCS
HCS
RSS
Parents,
providers
Immun. record
cards, providers
School
immunization cards
NIS Comparison year
2001
1995
1994
Age (months) of
children
19-35
19-35
19-35
Response rate (%)
64.2
32.3
Not reported
Estimated coverage
(%, 95% CI)
84
(79.7-88.3)
57
(50.7-64)
60
(58.9-61.6)
NIS-estimated
coverage (%, 95% CI)
74.3
(62.3-86.3)
79
(70.7-87.3)
68
(64.1-71.9)
Study design
Immunization
history source
HCS, Household Cluster Survey; RSS, Retrospective School Survey
Comparisons of Vaccine Coverage Estimates
Reference
Study design
Immunization
history source
NIS Comparison year
Age (months) of
children
Response rate (%)
Estimated coverage
(%, 95% CI)
NIS-estimated
coverage (%, 95% CI)
LA county (33)
Wu (34)
Hoban (35)
RSS
BCFBS
BCFBS
School immun.
cards
Providers, state
data system
Local health dep.,
parents, providers
1999
1996
2004
24
19-35
24
100.0
80.4
68.0
55
(not provided)
81
(79.1-82.9)
81.3
80.3
(68.1-92.5)
73.1
(62.3-83.9)
82.9
(71.5-94.3)
RSS, Retrospective School Survey; BCFBS, Birth Certificate Follow-back Survey
National Immunization Survey: Weaknesses
• Expected increase in cell-phone only and
broadband telephone households
• Sample size provides state or
Immunization Action Plan area data only
– Local community data unavailable
National Immunization Survey: Attributes
Interval from age 24 months until
survey results:
Standardization between states/study
populations?
Within state/study population
measures of coverage?
Proportion of children with completed
immunization information:
Antigens included:
Quality control?
Labor intensiveness:
Includes children who migrate into
area?
Includes children who migrate out of
area?
14-26 months
Yes
Yes, for 27 large Immunization Action
Plan areas
32.0% (2004)
All recommended by
ACIP/AAP/AAFP
Extremely good
Labor intensive – screening millions
of telephone numbers each year to
find eligible households
Yes
Yes (if in U.S.)
Future Opportunities and
Challenges for Measuring State and
Local Immunization Coverage
Population-based Retrospective
School Surveys
• Nearly all schools keep student
immunization records on file
• Technology permits automated entry
• Dates of vaccine administration and birth
dates could be forwarded to health
departments
Population-based Retrospective
School Surveys: Strengths
• Provide immunization histories for nearly
entire cohorts of children
• Coverage estimates available by school
and/or community
• Utilizes existing infrastructure
Population-based Retrospective
School Surveys: Weaknesses
• Practicality must be demonstrated
• Validity and completeness of school
immunization records must be researched
• Quality-control measures needed
• Lack of timeliness
• Limited ability to assess and compare
coverage between states
Immunization Registries
• Defined by NVAC as “confidential, computerized
information systems that contain information
about immunizations and children” 36
• Potential uses include 36
– Measuring vaccine coverage
– Generating reminders and recalls
– Identifying pockets of need for targeted interventions
– Improving vaccine safety
• Reducing overimmunization, calculating accurate
denominators for safety studies
– Facilitating vaccine inventory, supply, management
History of Immunization Registries
• Healthy People 2010 calls for 95%
participation of children under 6 in registries
• Substantial resources invested by federal
and state governments, non-profits
• 1993: Childhood Immunization Initiation
Act calls for national registry 37-39
– Language later changed to appropriate funding
for state and community registries
History of Immunization Registries
• Despite 10 years development, enrollment
still limited
– 2000: 24% of children under 6 participating 40
– 2003: participation increased to 44% 41
– 2003: 27 of 56 grantees had participation rates
above 64%
• Grantees represent 33% of U.S. children under 6
Immunization Registries: Weaknesses
• Participation, proportion public/private,
and completeness of immunization
histories vary by registry
• Registry records often incomplete
– According to NIS, 40% of records incomplete 42
– Completeness requires further study
• Coverage estimates generated lower than
NIS estimates 42
Immunization Registries: Attributes
Interval from age 24 months until
survey results:
Real time
Standardization between states/study
populations?
Potentially
Within state/study population
measures of coverage?
Proportion of children with completed
immunization information:
Antigens included:
Quality control?
Labor intensiveness:
Yes
Variable
All recommended by
ACIP/AAP/AAFP
Variable
NA
Includes children who migrate into
area?
Potentially
Includes children who migrate out of
area?
Potentially
Future Opportunities and
Challenges for Measuring
Immunization Coverage Nationally
National Coverage Assessment: Priorities
1. Monitor immunization coverage of
preschool children
2. Assess adolescent coverage
3. Maintain assessment of urban areas,
expand assessment to other urban and
rural areas
4. Maintain or improve response rates
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