Measuring Immunization Coverage among Pre-School Children: Past, Present and Future Opportunities Presented by

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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


  • 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

  • Ensure young children protected from vaccine-preventable diseases

  • Ensure rapid and equitable uptake of new vaccines

Indicators for Immunization Measurement among Preschoolers

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 outbreaks 5
    • Special interventions needed to improve local coverage

Measuring Immunization Coverage:

  • State and Local Methods

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

Retrospective School Surveys: Strengths 6

  • Capitalize on existing infrastructure

  • High completion rates

  • Include children who have migrated into study area

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

Birth Certificate Follow-back Surveys: Methods

  • Children born during specified time period randomly selected using birth certificates

  • Children located

  • 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

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.

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

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

    • Vaccine manufacturer reports
    • 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 preschoolers in 1980’s 12

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

National Immunization Survey: Strengths

  • Standardized coverage estimates allow for state comparisons

  • Survey infrastructure

  • Timeliness

Comparisons of Vaccine Coverage Estimates

Comparisons of Vaccine Coverage Estimates

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

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

Future Opportunities and Challenges for Measuring Immunization Coverage Nationally

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

References ___________

  • Ten great public health achievements—United States, 1900-1999. Morb Mortal Wkly Rep 1999;48:241-3.

  • Impact of vaccines universally recommended for children—United States, 1900-1998. MMWR Morb Mortal Wkly Rep 1999;48:243-8.

  • Luman ET, Barker LE, Shaw KM, et al. Timeliness of childhood vaccinations in the United States: days undervaccinated and number of vaccines delayed. JAMA 2005; 293:104-11.

  • Goldstein KP, Kviz FJ, Daum RS. Accuracy of immunization histories provided by adults accompanying preschool children to a pediatric emergency department. JAMA 1993; 270:2190-194.

  • Hutchins SS, Baughman AL, Orr M, et al. Vaccination levels associated with lack of measles transmission among preschool-aged population in the United States, 1989-1991. J Infect Dis 2004;189;(Supplement 1):S108-15.

  • Zell ER, Dietz V, Stevenson J, et al. Low vaccination levels of US preschool and school-age children. Retrospective assessments of vaccination coverage, 1991-1992. JAMA 1994;271:833-39.

References (cont.) __________________

  • 7. WHO Department of Vaccine and Biologicals. Description and comparison of the methods of cluster sampling and lot quality assurance sampling to assess immunization coverage. World Health Organization, Geneva. 2001. Available online at:

  • Simpson DM, Ezzati-Rice TM, Zell ER. Forty years and four surveys: how does our measuring measure up? Am J Prev Med 2001;20:6-14.

  • U.S. Department of Commerce, Bureau of the Census. Current Population Survey, September 1985: United States Immunization and Smoking Survey. Washington, DC, 1989. Codebook: CPH-009(1985). ICPSR Study No.: 9133.

  • Orenstein WA, Douglas RG, Rodewald LE, Hinman AR. Immunizations in the United States: Success, Structure, and Stress: A complex collaboration involving government, industry, providers, academe, professional societies, and third-party payers. Health Affairs 2005;24:599-611.

  • Chen RT, Orenstein WA. Epidemiologic Methods in Immunization Programs. Epidemiol Reviews 1996;18:99-117.

References (cont.) __________________

  • Measles Vaccination Levels among Selected Groups of Preschool-Aged Children—United States. MMWR Morb Mortal Wkly Rep 1991:40;36-9.

  • Cordero JF, Orenstein WA. The future of the National Immunization Survey. Am J Prev Med 2001;20:84-5.

  • Recommended childhood and adolescent immunization schedule-United States, 2006. MMWR Morb Mortal Wkly Rep 2005;54:Q1-4.

  • Grummer-Strawn LM, Li R. US National surveillance of breastfeeding behavior. J Hum Lact 2000;16:283-90.

  • Li R, Zhao Z, Mokdad A, et al. Prevalence of breastfeeding in the United States: the 2001 National Immunization Survey. Pediatrics 2003;111:1198-201.

  • Li R, Darling N, Maurice E, et al. Breastfeeding rates in the United States by characteristics of the child, mother, or family: the 2002 National Immunization Survey. Pediatrics 2005;115:e31-37.

  • Stanwyck CA, Kolasa MS, Shaw KM. Immunization requirements for childcare programs. Are they enough? Am J Prev Med 2004;27:161-63.

References (cont.) _________________

  • Davis MM, Gaglia MA. Associations of daycare and school entry vaccination requirements with varicella immunization rates. Vaccine 2005;23:3053-60.

  • LeBaron CW, Massoudi M, Stevenson J, Lyons B. Vaccination coverage and physician distribution in the United States, 1997. Pediatrics 2001;107:E31.

  • LeBaron CW, Lyons B, Massoudi M, Stevenson J. Childhood vaccination providers in the United States. Am J Public Health. 2002;92:266-270.

  • Jiles RB, Daniels D, Yusuf HR, et al. Undervaccination with hepatitis B vaccine: missed opportunities or choice? Am J Prev Med 2001;20:75-83.

  • Luman ET, Stokley S, Daniels D, Klevens RM. Vaccination visits in early childhood: just one more visit to be fully vaccinated. Am J Prev Med 2001;20:32-40.

  • Luman ET, McCauley MM, Stokley S, et al. Timeliness of childhood immunizations. Pediatrics 2002;110:935-39.

References (cont.) _________________

  • Gust DA, Strine TW, Maurice E et al. Underimmunization among children: effects of vaccine safety concerns on immunization status. Pediatrics 2004;114:e16-22.

  • Bardenheier B, Yusuf H, Schwartz B, et al. Are parental vaccine safety concerns associated with receipt of measles-mumps-rubella, diphtheria and tetanus toxoids with acellular pertussis, or hepatitis B vaccines by children? Arch Pediatr Adolesc Med 2004;158:569-75.

  • Massey JT. Estimation of the response rate in a telephone survey with screening. 1995 Proceedings of the Section on Survey Research Methods, Alexandria, VA: American Statistical Association, 1995, 653-58. Available online at:

  • Ezzati-Rice TM, Frankel MR, Hoaglin DC, et al. An alternative measure of response rate in random-digit-dialing surveys that screen for eligible subpopulations. J Econ Soc Meas 2000;26:99-109.

References (cont.) _________________

  • Council of American Survey Research Organizations. On the Definition of Response Rates: A Special Report of the CASRO Task Force on Completion Rates. Available online at:

  • Rosenthal J et al. Immunization Coverage Levels Among 19-to 35-month-old Children in 4 Diverse, Medically Underserved Areas of the United States. Pediatrics 2004;113:296-302.

  • Seattle-King County Department of Public Health and The University of Washington School of Public Health and Community Medicine. Household Immunization Survey of Central and Southeast Seattle April-August 1995, Final Report. Feb 1996.

  • Bastis DG, Jackson JF, Roche RA. Comparison of vaccine coverage levels from the National Immunization Survey and the Texas retrospective immunization survey. J Pub Heal Man Pract 2001;7;65-8.

  • County of Los Angeles Department of Health Services, Immunization Program. Expanded Kindergarten Retrospective Survey: 1996 & 1999. June 2001.

References (cont.) _________________

  • Oregon Immunization Program and Acute and Communicable Disease Epidemiology Program. 1999 Oregon Immunization Survey of Two-Year-Olds. Portland, OR, 2000. Available online at

  • Georgia Department of Human Resources, Division of Public Health, Epidemiology Branch, Prevention Branch, Immunization Program. Georgia Immunization Study, 2004 Final Report. Atlanta, GA, 2005. Available online at

  • National Vaccine Advisory Committee (NVAC). Development of community and state-based immunization registries; approved January 12, 1999. Atlanta, GA: US Department of Health and Human Services, CDC, 1999.

  • Freed GL, Katz SL. The Comprehensive Childhood Immunization Act of 1993. N Engl J Med 1993;329:1957-960.

References (cont.) _________________

  • Bill Summary and Status for the 103rd Congress S. 732. A bill to provide for the immunization of all children in the United States against vaccine-preventable disease, and for other purposes (as introduced (4/1/1993)). Sponsor: Sen Kennedy, Edward M. accessed April 26, 2006 from

  • Bill Summary and Status for the 103rd Congress S. 732. A bill to provide for the immunization of all children in the United States against vaccine-preventable disease, and for other purposes (as passed (11/4/1993)). Sponsor: Sen Kennedy, Edward M. Accessed April 26, 2006 from

  • Development of Community and State Based Immunization Registries Initiative on Immunization Registries. MMWR Morb Mortal Wkly Rep 2001:50(RR17).

  • Immunization Information System Progress - United States, 2003. MMWR Morb Mortal Wkly Rep 2005; 54:722-24.

  • Immunization Registry Progress—United States, January-December 2002. MMWR Morb Mortal Wkly Rep 2004:53;431-33.

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