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Pediatrics. 2016 May; 137(5): e20153755.
PMCID: PMC4845875

The Challenges in Measuring Local Immunization Coverage: A Statewide Case Study

Elizabeth Wolf, MD, MPH,corresponding authora,b,c Ali Rowhani-Rahbar, MD, MPH, PhD,d Jeffrey Duchin, MD,d,e M. Patricia DeHart, ScD,f and Douglas Opel, MD, MPHa,b

Abstract

There are many forms of existing immunization surveillance in the United States and Washington state, but all are limited in their ability to provide timely identification of clusters of unimmunized individuals and assess the risk of vaccine-preventable diseases. This article aims to: (1) describe challenges to measuring immunization coverage at a local level in the United States using Washington State as a case study; and (2) propose improvements to existing surveillance systems that address the challenges identified.

Case

As a pediatrician, you see a 12-month-old girl for her well-child visit. Her parents are unsure about giving her the measles-mumps-rubella vaccine. They are specifically concerned about measles and ask you if their daughter is really at risk for this disease. You tell them that although measles is not endemic to the United States, imported cases can occur at any time. You explain that the risk of developing measles depends on whether she comes into contact with someone who has measles, and that likelihood depends in part on the number of people around her who remain unimmunized. You try to look for local data regarding immunization coverage in their area, but give up because it is too difficult to find. Despite continued conversation with the family during the remainder of the visit about the importance of the measles-mumps-rubella vaccine, the parents ultimately decide against immunizing their daughter.

In early 2015, a traveler who had contracted measles overseas visited Disneyland while still infectious. Over the next 4 months, 189 people across 24 states subsequently developed measles.1,2 The scope of the outbreak was largely unanticipated since the United States and California, specifically, have high rates of immunization against measles. Before the outbreak, the proportion of children in California statewide who were adequately immunized against measles was 96% among children in daycare and 93% among children in kindergarten.3 During the investigation of the measles outbreak, however, public health officials discovered that among the 16 measles cases in California who were 1 to 3 years old, only 6 (38%) were vaccinated against measles and among the 2 measles cases who were 4 to 6 years old, none were vaccinated against measles (J. Zipprich, PhD, personal communication, 2015).

The Disneyland measles epidemic demonstrates once again that outbreaks of vaccine-preventable diseases (VPDs) can occur when unimmunized individuals cluster together despite high rates of overall immunization.4 Unimmunized individuals can spread VPDs by living in the same neighborhood,5 going to the same school,6,7 attending the same church8 or in the case of the Disneyland outbreak, frequenting the same tourist attraction.9 Existing surveillance systems often do not have enough granularity to detect these clusters of unvaccinated individuals. In fact, the World Health Organization has identified heterogeneity in immunization coverage as a major risk factor for the spread of VPDs and note that this heterogeneity may not be evident through routine monitoring.10

Lack of timely and accurate local immunization coverage information limits the ability of public health agencies to identify clusters of unimmunized children who might be susceptible to VPDs and prevents healthcare providers from gauging the risk of VPDs in their patients. In addition, as the case in the beginning of this article illustrates, lack of precise information about VPD risk can promote a so-called “ambiguity aversion” against immunizations in parents. Ambiguity aversion regarding immunizations occurs when missing or conflicting scientific risk information leads a person to construct their own subjective risk assessments, which maximize the risk of immunizations and minimize the risk of VPDs.11 This distorted risk assessment can therefore result in immunization refusal.

Like California, Washington state represents an opportunity to review challenges to childhood immunization surveillance, especially regarding the identification of clusters of underimmunized individuals. Washington has one of the highest nonmedical exemption rates for required kindergarten immunizations in the United States,12 and similar to California, there is wide variation in immunization coverage13 with proportions of unimmunized kindergarteners ranging from 0% to 50% among schools of different types and different geographic locations.14 This article aims to: (1) describe challenges to measuring immunization coverage at a local level in the United States using Washington state as a case study; and (2) propose improvements to existing surveillance systems that address the challenges identified.

Challenges to Existing Immunization Surveillance Systems

The National Immunization Survey is designed to capture immunization trends in all 50 states, the District of Columbia, and 27 other high-interest urban areas.15 Currently, only state-level estimates with relatively large margins of error are available for Washington State.16 To gauge smaller-scale immunization trends, 1 of 3 data sources is typically used: (1) an integrated healthcare delivery database, (2) school exemption data, or (3) a state immunization registry.

Integrated Healthcare Delivery Databases

Group Health and Kaiser Permanente are 2 examples of organizations that measure immunization uptake among their members in Washington state. These integrated healthcare databases can be quite useful in identifying clusters of unimmunized individuals who are enrolled in their plans.5 However, Group Health and Kaiser Permanente contain only 16% and 2% of Washington State’s market share, respectively.17 These databases typically include proportionally fewer low-income families and may not be generalizable to the entire state. Furthermore, these data are not typically available to individuals outside these organizations.

School Exemption Data

School exemption data make it possible for schools to identify which students are up to date with required immunizations, the proportion out of compliance but in the process of coming into compliance, and the proportion of students with immunization exemptions. Schools report their findings to the state, which, in turn, reports to the Centers for Disease Control and Prevention. Currently, all US states permit medical exemptions to immunization. Forty-seven states (with the exception of Mississippi, West Virginia, and, recently, California) also allow exemptions for religious reasons.18,19 Washington is 1 of 19 states that also permits philosophical exemptions.12,18 Washington State school exemption data can be helpful in understanding trends in reasons for immunization refusal (ie, medical, religious, or philosophical), and because these data are not subject to the same geographic and socioeconomic constraints as integrated healthcare databases, they are more generalizable.

Several problems exist with school exemption data quality, however, and these problems often vary by state. First, Washington is 1 of a few states that permit school data to be entered by families themselves, which can result in inaccuracies.20 Second, reporting of school data often occurs before final immunization statuses are complete (thus leading to potential underestimates of coverage). Third, most states do not include homeschooled children in their school exemption data21; yet, vaccine refusal can be particularly pronounced among families that homeschool,22,23 and VPDs are known to occur in these settings.23,24 Fourth, exemption data from private schools, though required by law, can be more difficult to obtain. The logistic capability required to record and track immunization data is frequently lacking in private schools (L. Page, MPH, personal communication, 2016). This can be a substantial problem because certain private schools, although accounting for a relatively small fraction of all students, usually have higher proportions of underimmunized children.25 Lastly, budgetary constraints and inadequate staffing can prevent sufficient follow-up of underimmunized children.26,27

State Immunization Registries

An alternative to school exemption data is a state immunization registry, also known as an immunization information system (IIS). IIS’s are “confidential, computerized, population-based systems that collect and consolidate immunization data from immunization providers.”28 The Washington State Immunization Information System (WAIIS) is populated by birth certificates and includes every child born in Washington State. State registries are not subject to the same age limitations as school exemption data. In addition, data are generally entered by medical staff at the time that immunizations are given, so the databases are kept relatively up-to-date. There has been a notable increase in the use of state immunization registries in the past decade within Washington29 and across the United States,28 driven by the Affordable Care Act and so-called “meaningful use” incentives.30

There are, however, limitations to WAIIS and the other state-based registries. First, although participation, based on the percentage of children ≤6 years old with ≥2 immunizations, is high (96%) in WAIIS, it is as low as 16% in some state registries.31 Indeed, New Hampshire is still in the process of establishing its IIS.32 Second, what data are contained in a state immunization registry varies from state to state. Many registries, for example, do not record the child’s school, which can make outbreak investigation quite challenging. Third, because registries operate at the state, rather than national, level, it is often impossible to distinguish between an underimmunized child and one who has simply moved out of state.

Improving Immunization Surveillance

Establishment of a National Immunization Registry

One way to improve immunization surveillance is to establish a national registry. The Childhood Immunization Initiative Act of 1993 was originally introduced to Congress with language to do just this, but this language was later changed to instead allocate funding for states to establish their own registries.20,33 The main benefit of a national registry is that it can help medical and public health officials more easily gauge local trends in immunization and detect clusters of unimmunized individuals.34 This is evident from the experience of countries with national immunization registries, including Australia and many countries in Western Europe.35 In the United Kingdom, for example, all administered immunizations are linked to local and national public health systems. Immunization data can also be disaggregated based on clinical characteristics or location. In the event of an epidemic, general practitioners can interrogate the system and contact underimmunized individuals (D. Salisbury, CB, FRCP, personal communication, 2015). Some national registries can also be linked with disease surveillance to help detect adverse events after immunization.36

Although well suited for surveillance purposes, a national immunization registry is unlikely to be established in the United States in the near future. The 10th amendment is frequently interpreted as allowing states to control their own immunization registries,37 and 15 states have statutes that specifically prohibit immunization data sharing outside of their own jurisdictions.38,39 There are also several antivaccination groups that oppose a national registry out of fear of being “tracked” by the government.40,41

Strengthening and Integrating State Immunization Registries

As an alternative strategy to establishing a national immunization registry, the federal government is attempting to strengthen and standardize state registries.42 The National Vaccine Advisory Committee established functional standards for state immunization systems in 2001, which were updated recently by the Centers for Disease Control and Prevention.43 These standards outline data quality goals and recommend that information should be available “to a wide range of stakeholders, including public and private care providers, public health programs, emergency responders, and many others.” However, access to registry data by local health jurisdictions, physicians, and the general public can be quite limited since stakeholders are dictated by state law.43

Ideally, state registries would be compatible with one another and able to share information so that national assessments could be made and account for individuals moving from state to state.44 Currently, 36 states permit immunization data to be shared between states and 29 of these report active data sharing data across state lines.38 To expand data sharing between states, the nonprofit, Every Child by Two, in conjunction with the Department of Health Policy at George Washington University, drafted a model statute for data sharing that can be adopted by each individual state. Some groups have proposed the creation of a single data sharing agreement for all states similar to that governing the North American Association of Central Cancer Registries.39 In 2014, the Office of the National Coordinator for Health Information Technology launched a pilot program to exchange immunization data between Oregon and Washington State (2 states that had pre-existing data exchange agreements) through an Office of the National Coordinator for Health Information Technology–developed data hub.39,45 This pilot program will allow for bidirectional data queries and real-time data sharing between the 2 states.46 In the future, other states with compatible systems may also be connected to this data hub.

Enhancing School Exemption Data

In addition to improving the quality, accessibility, and compatibility of state registries, a key component to improving immunization surveillance is providing support to schools to improve the accuracy and timeliness of exemption data. There is also a need to enhance reporting and enforcement of state immunization requirements in younger children because outbreaks of VPDs are known to occur in early child care settings,47 and younger children can be at particularly high risk of complications from VPDs.48 Improving immunization coverage in early child care settings has even been shown to reduce the morbidity of VPDs in household contacts.49 Although all states have immunization requirements for licensed daycares, head start programs, and preschools, there is currently great variability in the reporting and enforcement of these requirements.3,5052

Predicting Risk of VPD

Because state registries typically include an individual’s address, geospatial statistical techniques could be employed to identify underimmunized “hotspots.” A good illustration of these techniques is a study that assessed the relationship between immunization and proximity to pediatric providers using the Washington, DC Immunization Information System.53 Geospatial techniques could also be used to gather the data necessary to develop highly specific prediction models regarding which individuals are at risk for a VPD during an outbreak, because these predictions not only include the proportion of unimmunized (susceptible) individuals within a population, but also how likely susceptible individuals are to come into contact with one another.

Conclusions

There are many forms of existing immunization surveillance in the United States and Washington state, but all are limited in their ability to provide the timely identification of geographic clusters of unimmunized individuals and assess the risk of VPDs. Yet, these 2 features are emerging as important components of public health and clinical practice. Other developed countries are able to use national immunization registries to efficiently identify clusters of unimmunized individuals that are at risk for outbreaks of VPDs. In the absence of widespread support for such a national immunization registry within the United States, there should be renewed support for state and federal programs that enhance school exemption data and improve and integrate state immunization registries.

Glossary

IIS
immunization information system
VPD
vaccine-preventable disease
WAIIS
Washington State Immunization Information System

Footnotes

Contributed by

Dr Wolf conceptualized, researched, drafted, revised, and approved the final version of the manuscript; Drs Rowhani-Rahbar and Opel conceptualized, contributed to, revised, and approved the final version of the manuscript; and Drs Duchin and DeHart contributed to, revised, and approved the final version of the manuscript.

FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.

FUNDING: Dr Wolf received salary support from Ruth L. Kirschstein National Research Service Award, National Institutes of Health grant T32HP10002. There was no funding specific to this project. Funded by the National Institutes of Health (NIH).

POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest relevant to this article to disclose.

References

1. Centers for Disease Control and Prevention. Measles Cases and Outbreaks. Available at: www.cdc.gov/measles/cases-outbreaks.html. Accessed May 7, 2015
2. Zipprich J, Winter K, Hacker J, Xia D, Watt J, Harriman K; Centers for Disease Control and Prevention (CDC) . Measles outbreak--California, December 2014-February 2015. MMWR Morb Mortal Wkly Rep. 2015;64(6):153–154 [PubMed]
3. Immunization Levels in Child Care and Schools 2015; www.cdph.ca.gov/programs/immunize/Pages/ImmunizationLevels.aspx. Accessed May 14, 2015
4. May T, Silverman RD. ‘Clustering of exemptions’ as a collective action threat to herd immunity. Vaccine. 2003;21(11-12):1048–1051 [PubMed]
5. Lieu TA, Ray GT, Klein NP, Chung C, Kulldorff M Geographic clusters in underimmunization and vaccine refusal. Pediatrics. 2015;135(2):280–289 [PubMed]
6. Omer SB, Enger KS, Moulton LH, Halsey NA, Stokley S, Salmon DA. Geographic clustering of nonmedical exemptions to school immunization requirements and associations with geographic clustering of pertussis. Am J Epidemiol. 2008;168(12):1389–1396 [PubMed]
7. Atwell JE, Van Otterloo J, Zipprich J, et al. Nonmedical vaccine exemptions and pertussis in California, 2010. Pediatrics. 2013;132(4):624–630 [PubMed]
8. Silverman L. Texas megachurch at center of measles outbreak. National Public Radio. 2014. Available at: www.npr.org/2013/09/01/217746942/texas-megachurch-at-center-of-measles-outbreak. Accessed December 3, 2015
9. Gardy JL, Naus M, Amlani A, et al. . Whole-genome sequencing of measles virus genotypes h1 and d8 during outbreaks of infection following the 2010 Olympic Winter Games reveals viral transmission routes. J Infect Dis. 2015;212(10):1574–1578 [PubMed]
10. World Health Organization. Global Measles and Rubella Strategic Plan 2012–2020. . Available at: http://measles.wpengine.com/wp-content/uploads/2013/06/Measles-Rubella-Strategic-Plan.pdf. Accessed August 13, 2015
11. Blaisdell LL, Gutheil C, Hootsmans NA, Han PK. Unknown Risks: Parental Hesitation about Vaccination [published online ahead of print October 27, 2015]. Med Decis Making. doi:10.1177/0272989X15607855 [PubMed]
12. Seither R, Masalovich S, Knighton CL, Mellerson J, Singleton JA, Greby SM; Centers for Disease Control and Prevention (CDC) Vaccination coverage among children in kindergarten - United States, 2013-14 school year. MMWR Morb Mortal Wkly Rep. 2014;63(41):913–920 [PubMed]
13. Washington State Department of Health Office of Immunization & Child Profile Summary of Immunization Coverage for Kindergarten by County for School Years 2003–04 through 2012–2013.Available at: www.doh.wa.gov/Portals/1/Documents/Pubs/348-242-ImmsCoverageKinderCounty.pdf. Accessed January 28, 2014
14. Washington State Department of Health. Kindergarten School Immunization Coverage by School District for School Year 2013–2014. Available at: www.doh.wa.gov/DataandStatisticalReports/HealthBehaviors/Immunization/SchoolReports%20-%20data. Accessed May 7, 2015
15. Zell ER, Ezzati-Rice TM, Battaglia MP, Wright RA. National Immunization Survey: the methodology of a vaccination surveillance system. Public Health Rep. 2000;115(1):65–77 [PMC free article] [PubMed]
16. Centers for Disease Control and Prevention. Areas Sampled Separately in the National Immunization Survey (NIS) Available at: www.cdc.gov/vaccines/imz-managers/coverage/nis/child/qa-faqs-tables.html. Accessed May 7, 2015
17. Washington State Rate Analysis Carriers with Low 2014 Market Share Hold Down Premiums in 2015. Available at: http://avalere.com/expertise/managed-care/insights/washington-state-rate-analysis-carriers-with-low-2014-market-share-hold-dow. Accessed June 15, 2015
18. Yang YT, Silverman RD. Legislative prescriptions for controlling nonmedical vaccine exemptions. JAMA. 2015;313(3):247–248 [PubMed]
19. Firger J. California Governor Signs Vaccine Exemption Law. Newsweek 2015. Available at: www.newsweek.com/california-governor-signs-vaccine-exemption-law-348926. Accessed August 28, 2015
20. Salmon DA, Smith PJ, Navar AM, et al. Measuring immunization coverage among preschool children: past, present, and future opportunities. Epidemiol Rev. 2006;28(1):27–40 [PubMed]
21. Khalili D, Caplan A. Off the grid: vaccinations among homeschooled children. J Law Med Ethics. 2007;35(3):471–477 [PubMed]
22. Kennedy AM, Gust DA. Parental vaccine beliefs and child’s school type. J Sch Health. 2005;75(7):276–280 [PubMed]
23. Kennedy AM, Gust DA. Measles outbreak associated with a church congregation: a study of immunization attitudes of congregation members. Public Health Rep. 2008;123(2):126–134 [PMC free article] [PubMed]
24. Johnson MG, Bradley KK, Mendus S, Burnsed L, Clinton R, Tiwari T Vaccine-preventable disease among homeschooled children: Two cases of tetanus in Oklahoma. Pediatrics. 2013;132(6). Available at: www.pediatrics.org/cgi/content/full/132/6/e1686 [PubMed]
25. Shaw J, Tserenpuntsag B, McNutt LA, Halsey N. United States private schools have higher rates of exemptions to school immunization requirements than public schools. J Pediatr. 2014;165(1):129–133 [PubMed]
26. Rubin J. Fewer Ill Students Can Visit the School Nurse. Los Angeles Times 2005. Available at: http://articles.latimes.com/print/2005/mar/20/local/me-nurse20. Accessed September 10, 2015
27. Lin R., II Measles outbreak Q&A: Some schools breaking law on vaccinations. Los Angeles Times 2015. Available at: http://touch.latimes.com/ - section/-1/article/p2p-82701756/. Accessed September 10, 2015
28. Centers for Disease Control and Prevention . Progress in immunization information systems - United States, 2012. MMWR Morb Mortal Wkly Rep. 2013;62(49):1005–1008 [PubMed]
30. Centers for Disease Control and Prevention. Immunization Information Systems (IIS): Meaningful Use and Immunization Information Systems. Available at: www.cdc.gov/vaccines/programs/iis/meaningful-use/mu-steps-ir-stage1.html. Accessed October 7, 2013
31. Centers for Disease Control and Prevention. 2013 IISAR Data Participation Rates. Available at: www.cdc.gov/vaccines/programs/iis/annual-report-IISAR/2013-data.html - child. Accessed August 13, 2015
32. Department of Health and Human Services. Meaningful Use in the Division of Public Health Services Immunization Data. Available at: www.dhhs.nh.gov/dphs/bphsi/meaningful-use.htm. Accessed Sept. 23, 2015
33. Freed GL, Katz SL. The Comprehensive Childhood Immunization Act of 1993. N Engl J Med. 1993;329(26):1957–1960 [PubMed]
34. Gostin LO, Lazzarini Z. Childhood immunization registries. A national review of public health information systems and the protection of privacy. JAMA. 1995;274(22):1793–1799 [PubMed]
35. Pebody R.. Vaccine registers--experiences from Europe and elsewhere. Euro Surveill. 2012;17(17):20159. [PubMed]
36. Buttery JP, Danchin MH, Lee KJ, et al. Intussusception following rotavirus vaccine administration: Post-marketing surveillance in the National Immunization Program in Australia. Vaccine 29(16):3061–3066 [PubMed]
37. Urquhart G. Progress on the horizon to implement ‘lifelong’ immunization registries. Infectious Disease News 2014. Available at: www.healio.com/infectious-disease/news/print/infectious-disease-news/%7B5aa0df49-3774-45f1-bda2-dc2f89bb1633%7D/progress-on-the-horizon-to-implement-lifelong-immunization-registries. Accessed September 23, 2015
38. Martin DW, Lowery NE, Brand B, Gold R, Horlick G. Immunization information systems: a decade of progress in law and policy. J Public Health Manag Pract. 2015;21(3):296–303 [PMC free article] [PubMed]
39. The Network for Public Health Law. Memorandum: Legal issues related to cross-jurisdictional sharing of state immunization information system data. Available at: www.astho.org/Public-Policy/Public-Health-Law/Cross-Jurisdictional-Sharing-IIS-Data. Accessed September 23, 2015
40. Fisher B. Tracking System and Privacy. Available at: www.nvic.org/vaccine-laws/tracking-system-and-privacy/the-national-electronic-tracking-registry.aspx. Accessed May 7, 2015
41. Richardson D. Government Immunization Registries - A Threat to Privacy and Freedom. Available at: www.vaccineinfo.net/issues/tracking/nationalregistry/nationalstatement.shtml. Accessed May 7, 2015
42. Centers for Disease Control and Prevention (CDC) . Progress in immunization information systems--United States, 2011. MMWR Morb Mortal Wkly Rep. 2013;62(3):48–51 [PubMed]
43. Immunization Information System Functional Standards 2013-2017. 2012; www.cdc.gov/vaccines/programs/iis/func-stds.pdf. Accessed May 18, 2015
44. Hinman AR, Urquhart GA, Strikas RA; National Vaccine Advisory Committee . Immunization information systems: National Vaccine Advisory Committee progress report, 2007. J Public Health Manag Pract. 2007;13(6):553–558 [PubMed]
45. American Immunization Registry Association Snapshots: Immunization Registry News from American Immunization Registry Association. http://www.immregistries.org/attachments/NewsArticle_SnapShot (Dec 14).pdf. Published December 2014. Accessed May 7, 2015
46. Department of Health and Human Services The Annual Report of the State of the National Vaccine Plan 2014. Available at: www.hhs.gov/nvpo/vacc_plan/annual-report-2014/nationalvaccineplan2014.pdf. Accessed May 7, 2015
47. Hutchins SS, Escolan J, Markowitz LE, et al. Measles outbreak among unvaccinated preschool-aged children: Opportunities missed by health care providers to administer measles vaccine. Pediatrics. 1989;83(3):369–374 [PubMed]
48. Hussey GD, Klein M. A randomized, controlled trial of vitamin A in children with severe measles. N Engl J Med. 1990;323(3):160–164 [PubMed]
49. Hurwitz ES, Haber M, Chang A, et al. . Effectiveness of influenza vaccination of day care children in reducing influenza-related morbidity among household contacts. JAMA. 2000;284(13):1677–1682 [PubMed]
50. Whaley L. Vaccination rates low at Los Angeles County preschools and day care centers. Los Angeles Daily News 2015. www.dailynews.com/health/20150322/vaccination-rates-low-at-los-angeles-county-preschools-and-day-care-centers. Accessed September 10, 2015
51. Office for State, Tribal, Local and Territorial Support, Centers for Disease Control. State School Immunization Requirements and Vaccine Exemption Laws. Available at: www.cdc.gov/phlp/docs/school-vaccinations.pdf. Accessed May 7, 2015
52. National Foundation for Infectious Disease Flu in Day Care: The Impact of Vaccination Requirements. Available at: www.nfid.org/day-care-report. Accessed May 7, 2015
53. Fu LY, Cowan N, McLaren R, Engstrom R, Teach SJ Spatial accessibility to providers and vaccination compliance among children with medicaid. Pediatrics. 2009;124(6):1579–1586 [PubMed]

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