Measuring Immunization Coverage among Pre-School 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. It’s 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; 28:27-40

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 outbreaks5 • 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: Strengths6 • 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 1980’s 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

30. 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

34. National Immunization Survey Response Rates, 1995–2004 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

45. 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

46. 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___________ • 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.