Journal Issue: Children and Divorce Volume 4 Number 1 Spring/Summer 1994
Assessing the immunization coverage of young children in the United States is quite difficult. Some countries with national health systems maintain computerized immunization registers that can be used both to monitor the immunization status of the population and to track children who are not meeting recommended schedules for vaccination. The closest arrangement to such a data system in the United States is the disease surveillance system which, by monitoring the incidence of vaccine-preventable diseases, can identify gaps in immunization coverage after they occur and help characterize high-risk populations.
In addition, because children are required to provide proof of immunization status at time of entry into school in all states, data collected at school entry can provide retrospective estimates of the immunization status of young children, although the information will be three to four years out of date and perhaps subject to substantial error.7
The United States has relied, intermittently, on national survey data to provide timely estimates of the immunization status of young children.7 Through 1985, information on immunization status was collected in the United States Immunization Survey (USIS). This survey was a section of the annual Current Population Survey conducted by the Bureau of the Census.
The USIS was suspended after 1985, but following large outbreaks of measles in the late 1980s, national immunization surveillance was reinstated by adding questions on immunization status to the National Health Interview Survey (NHIS) in 1991. The NHIS is administered annually to approximately 50,000 households. Data from the NHIS immunization sample are presented in this article and are based on information about the immunization status of only one child aged 0 to 5 years per survey household. Information was obtained from a written immunization record if the record was available.
Written immunization records may have been supplemented by adult oral recall information, and if written records could not be produced, the information on immunizations was based completely on adult recall. Information on DTP/DT, polio, MMR/measles, and Hib vaccines are included in the 1991 survey.7 The NHIS immunization survey component was also conducted in 1992.
The NHIS immunization survey is useful for monitoring national trends but of limited value in implementing remedial programs. The survey is not designed to provide reliable estimates at the state and local level or to give reliable estimates for narrow age groups. There also is a time delay of more than a year between the time survey data are initially collected and the time they become generally available.
Beginning in 1994, as discussed below, new modalities of data collection will be implemented to measure immunization coverage at various levels, from national down to individual clinics. Some data will be reported quarterly.5