Measuring Immunization Coverage among PreSchool Children: Past, Present and Future Opportunities

1
Measuring Immunization Coverage among Pre-School
Children Past, Present and Future Opportunities

• Presented by
• Daniel A. Salmon, PhD, MPH

2
Department of Epidemiology and Health Policy
Research, College of Medicine, University of
Florida, Gainesville, FloridaInstitute for
Vaccine Safety Department of International
Health, Johns Hopkins Bloomberg School of Public
Health, Baltimore, Maryland
3
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. Its very exciting!

4
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 2827-40

5
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

6
Rationale for Measuring Immunization Coverage
among Preschoolers

• Ensure young children protected from
  vaccine-preventable diseases
• Ensure rapid and equitable uptake of new vaccines

7
Indicators for Immunization Measurement among
Preschoolers

• Age-appropriate vaccination status
• Up-to-date vaccination status 3

8
Measuring Immunization Coverage among Preschoolers

• Parental recall of vaccination often inaccurate4
• Age at measurement varies

9
Immunization Measurement among Preschoolers

• Local measurement useful
• Pockets of low-coverage susceptible to outbreaks
  5
• Special interventions needed to improve local
  coverage

10
Measuring Immunization Coverage

• State and Local Methods

11
Retrospective School Surveys Methods

• 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

12
Retrospective School Surveys Strengths 6

• Capitalize on existing infrastructure
• High completion rates
• Include children who have migrated into study area

13
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

14
Retrospective School Surveys Attributes
15
Birth Certificate Follow-back Surveys Methods

• Children born during specified time period
  randomly selected using birth certificates
• Children located
• Immunization histories collected

16
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

17
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

18
Birth Certificate Follow-back Surveys Attributes
19
Household Cluster Surveys Methods 7

• Regions divided into non-overlapping clusters
• Clusters sampled
• Households contacted until sufficient number
  identified within each cluster
• Obtain immunization histories of children in
  household.

20
Household Cluster Surveys Strengths

• Efficient
• Coverage estimates valid for individual clusters
• Coverage can be compared from one region to
  another

21
Household Cluster Surveys Weaknesses

• Costly in rural areas
• Validity questionable if immunization histories
  not verified
• Methodology prone to bias

22
Household Cluster Surveys Attributes
23
Measuring Immunization Coverage

• National Surveys

24
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

25
History of National Immunization Coverage
Measurement

• CDC begins passively monitoring vaccine
  uptake8,10, 11
• Vaccine manufacturer reports
• Biologics Surveillance System

26
History of National Immunization Coverage
Measurement

• CDC conducted retrospective school surveys
• Found association between lower immunization
  rates and increased measles incidence in
  preschoolers in 1980s 12

27
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

28
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

29
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

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National Immunization Survey

• Survey results assist in
• Determining national vaccine needs
• Determining level of state funding

31
National Immunization Survey Methods

• Quarterly surveys conducted in 78 Immunization
  Action Plan areas
• Phases of data collection
• List-assisted, random-digit dialing survey
• National Immunization Survey Provider Record
  Check survey

32
National Immunization Survey Strengths

• Standardized coverage estimates allow for state
  comparisons
• Survey infrastructure
• Timeliness

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(No Transcript)
34
National Immunization Survey Response Rates,
19952004
In 2004, the product of these three proportions
was 32.0 29
35
Comparisons of Vaccine Coverage Estimates
HCS, Household Cluster Survey RSS, Retrospective
School Survey
36
Comparisons of Vaccine Coverage Estimates
RSS, Retrospective School Survey BCFBS, Birth
Certificate Follow-back Survey
37
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

38
National Immunization Survey Attributes
39
Future Opportunities and Challenges for Measuring
State and Local Immunization Coverage
40
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

41
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

42
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

43
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

44
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

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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

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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

47
Immunization Registries Attributes
48
Future Opportunities and Challenges for Measuring
Immunization Coverage Nationally
49
National Coverage Assessment Priorities

• Monitor immunization coverage of preschool
  children
• Assess adolescent coverage
• Maintain assessment of urban areas, expand
  assessment to other urban and rural areas
• Maintain or improve response rates

50
References___________

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