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Immunization Information Systems Progress --- United States, 2006

A CDC program goal for 2010 is to achieve >95% participation in an immunization information system (IIS) (defined as having two or more recorded vaccinations) among children aged <6 years. IISs, previously known as immunization registries, are confidential, computerized information systems that collect and consolidate vaccination data from multiple health-care providers, generate reminder and recall notifications, and assess vaccination coverage within a defined geographic area (1). Most IISs have additional capabilities, such as vaccine management, adverse event reporting, maintenance of birth-to-death vaccination histories, and interoperability with other health information systems (1). IISs can provide accurate data on which to make informed vaccination decisions and better protect against vaccine-preventable diseases (2). This report highlights selected data from CDC's 2006 Immunization Information System Annual Report (IISAR), a survey of grantees in 50 states, five cities,* and the District of Columbia that receive funding under the Public Health Service Act. The data indicated that 65% of all U.S. children aged <6 years (approximately 15 million children) participated in an IIS in 2006, an increase from 56% in 2005 (1). The majority of grantees (70%) reported that their IISs have the capacity to track vaccinations for persons of all ages. Data on vaccinations were entered within 30 days of vaccine administration for 69% of children aged <6 years. However, results for certain data completeness measures were low. These findings underscore the need to continue to address challenges to full IIS participation and ensure high-quality information.

The 2006 IISAR, a self-administered, Internet-based questionnaire, was made available to immunization program managers as part of an annual reporting requirement. As in previous years, respondents were asked about the number of children aged <6 years participating in an IIS, the number of health-care--provider sites participating in an IIS, and other programmatic and technical capabilities (e.g., data linkages with other health information systems, data use, vaccine management, software and hardware capabilities, and report functions). All 56 grantees were asked to complete the IISAR; 51 reported on the number of children aged <6 years participating in an IIS during 2006. The percentage of all U.S. children aged <6 years participating in an IIS was calculated by dividing the number of children aged <6 years participating in an IIS reported by the 51 grantees by the 2006 mid-year U.S. Census projection for all children aged <6 years.

In 2006, approximately 15 million (65%) U.S. children aged <6 years participated in an IIS. Fifteen (27%) grantees reported that >95% of children aged <6 years participated in an IIS (Figure), and 10 (18%) grantees reported participation ranging from 81% to 94%. Data also were reported for participation of persons aged >6 years. Forty-seven (84%) grantees reported maintaining vaccination data in their IIS for persons aged 11--18 years, of whom approximately 22.3 million (66%) had two or more vaccinations recorded in an IIS. In addition, 39 (70%) grantees reported having capacity to maintain vaccination data from birth to death, with 33.5 million (18%) persons aged >19 years in the United States having one or more vaccinations recorded in an IIS.

IIS data quality measures include the timeliness of vaccination data submission to an IIS and two measures of completeness of National Vaccine Advisory Committee (NVAC) core data elements (3). The first measure assesses the proportion of core data fields that are populated consistently in the IIS, and the second is a proxy measure for completeness of vaccination history for each IIS participant. The timeliness standard specifies that all vaccine doses for children aged <6 years should be recorded in a grantee IIS within 30 days of administration. IISAR data for 2006 indicated that 69% of vaccine doses for children aged <6 years were recorded in a grantee IIS within 1 month of administration, 11% within 31--60 days, and 20% more than 60 days after administration.

Completeness of data is measured by examining each of 14 standardized core data elements to determine the proportion that are completed in >90% of records. These 14 standardized core data elements, approved by NVAC (3,4), include demographic and vaccine event information. The core data elements are designed to standardize a set of patient demographic and vaccine event elements that are necessary for data exchanges between IISs, identification and removal of duplicate records, and exchanges with other health information systems (3,4). Collectively among responding grantees, data were reported for six of 14 core data elements in >90% of IIS records (Table), including four of seven patient core data elements and two of four vaccine core data elements, but none of three maternal core data elements.

Completeness of data in IISs also is gauged by the proportion of children aged 19--35 months participating in an IIS who were recorded as having received the complete 4:3:1:3:3 series§ of recommended vaccine doses. IISAR data for 2006 indicate that of the 3.7 million (62%) children aged 19--35 months participating in an IIS, an estimated 1.8 million (48%) had complete histories for the full 4:3:1:3:3 vaccination series. Although not directly comparable, this is lower than the estimated proportion (>75%) of children reported by the National Immunization Survey (NIS) to have received the same vaccination series (5). Completeness of IIS vaccination histories varies substantially by state; however, nine grantees have complete 4:3:1:3:3 vaccination series that are comparable to traditional coverage survey rates for 2006.

Reported by: G Urquhart, MPH, B Rasulnia, PhD, J Kelly, Immunization Svcs Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:

IISs are used increasingly for managing vaccine inventories, identifying pockets of need (i.e. specific geographic areas within state or urban jurisdictions that contain large numbers of children who are either under-immunized or at risk for under-immunization), tracking vaccination histories for outbreaks and public health emergencies, and measuring uptake of newly recommended vaccines (4,6--8). The findings in this report illustrate two major challenges for IISs: 35% of U.S. children aged <6 years are not participating in an IIS, and the data on participating children is not reported completely and in a timely manner.

CDC is pursuing three major strategies to address these challenges and ensure that the 2010 program goal of >95% IIS child participation is achieved. First, CDC implemented an enhanced technical assistance project, in collaboration with the Public Health Informatics Institute, to provide planning support services to grantees with low child-participation rates (<33%). Second, CDC has been encouraging CDC grantees to increase IIS child-participation rates by promoting IIS data use by health-care providers, schools, and health plans. IIS data are used increasingly by school district administrative staff to assess compliance with school immunization laws. Increased use of IIS data by school districts reduces the number of requests to provider practices for records of students who have been vaccinated. By reporting complete and accurate vaccination data to an IIS, practices can reduce staff time required to produce or locate vaccination records or certificates (4). A third strategy to increase IIS child-participation rates is to promote health plan use of IIS data for Health Plan Employer Data and Information Set (HEDIS) vaccination coverage measures, in lieu of using more costly chart reviews. HEDIS is a tool used by >90% of health plans in the United States to measure performance on selected criteria of care and services, including vaccinations (9).

CDC has validated the usefulness of IIS data in supplementing NIS data, but noted that the quality and completeness of the registry data must be improved and must be comparable across all states before consideration can be given to supplement or replace provider-reported data in NIS (10). The low percentages for five NVAC core data elements might be the result of IIS use of billing system data rather than more complete medical records. Billing systems often do not collect core data elements such as vaccine manufacturer and lot number, and mother's first, maiden, and last names, which are needed to improve vaccination data quality. CDC will promote increased interoperability between IISs and electronic medical record (EMR) systems through use of updated Health Level Seven messaging standards and reduced use of clinical billing systems data. Measures are under way to ensure that EMR standards for vaccination data facilitate links between EMR systems and IISs, thus facilitating recording of vaccination data in IIS.

The findings in this report are subject to at least two limitations. First, data from the 2006 IISAR are self-reported, which might have resulted in reporting bias. Grantees might, for example, miscalculate totals provided in response to some questions on the annual survey, although observations during site visits have found little or no bias. Second, because some grantees did not report data, the IIS participation rates for children aged <6 years and providers might be underestimated. Several grantees that had good responses in previous years missed reporting because they were installing new software programs.

As IISs continue to expand their capacity to collect information on persons of all ages, they will be important in assessing national vaccination coverage levels, identifying pockets of need, tracking vaccinations for outbreaks and public health emergencies, monitoring vaccine uptake for newly introduced vaccines or pandemic influenza vaccine, and managing vaccine inventories (4,6--8). This report underscores the need for continued efforts to improve child participation and to ensure that IISs meet data quality measures for timeliness and completeness.


  1. CDC. Immunization information system progress---United States, 2005. MMWR 2006;55:1327--29.
  2. CDC. Immunization registry strategic plan, 2002--2007. Atlanta, GA: US Department of Health and Human Services, CDC; 2003. Available at
  3. National Vaccine Advisory Committee. Development of community and state-based immunization registries: report of the National Vaccine Advisory Committee (NVAC). Atlanta, GA: US Department of Health and Human Services, CDC; 1999. Available at
  4. Hinman AR, Urquhart GA, Strikas RA, and the National Vaccine Advisory Committee. Immunization information systems: National Vaccine Advisory Committee progress report, 2007. J Public Health Manag Pract 2007;13:553--8.
  5. Wooten KG, Darling N, Singleton JA, Shefer A. National, state, and local area vaccination coverage among children aged 19--35 months---United States, 2006. MMWR 2007;56:880--5.
  6. Bartlett DL, Washington ML, Bryant A, Thurston N, Perfili CA. Cost savings associated with using immunization information systems for vaccines for children administrative tasks. J Public Health Manag Pract 2007;13:559--66.
  7. Enger KS, Stokley S. Meningococcal conjugate vaccine uptake, measured by Michigan's immunization registry. J Adolesc Health 2007;40:398--404.
  8. Boom JA, Dragsbaek AC, Nelson CS. The success of an immunization information system in the wake of Hurricane Katrina. Pediatrics 2007;119:1213--7.
  9. National Committee for Quality Assurance. What is HEDIS? Available at
  10. Khare M, Piccinino L, Barker LE, Linkins RW. Assessment of immunization registry databases as supplemental sources of data to improve ascertainment of vaccination coverage estimates in the National Immunization Survey. Arch Pediatr Adolesc Med 2006;160:838--42.

* Chicago, Illinois; Houston, Texas; New York, New York; Philadelphia, Pennsylvania; and San Antonio, Texas.

42 USC Sect. 247b, Project grants for preventive health services.

§ 4 doses diphtheria and tetanus toxoids and acellular pertussis vaccines, 3 doses poliovirus vaccine, 1 dose measles, mumps, and rubella vaccine, 3 doses Haemophilus influenzae type B vaccine, and 3 doses hepatitis B vaccine.

Health Level Seven is an accredited organization that develops standards for the exchange of electronic health-care data. Additional information is available at


TABLE. Percentage of records in immunization information
systems with core data elements* that contain data — United
States, 2006†
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FIGURE. Percentage of children aged <6 years participating*
in a grantee† immunization information system — United
States, five cities, and the District of Columbia,§ 2006
Return to top.

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Date last reviewed: 3/19/2008


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