The National Immunization Survey (NIS) produces high-quality estimates on the rate of immunization among young children in the U.S., considered a critical contributor to the prevention of childhood diseases. Administered by NORC at the University of Chicago since 2005, the NIS is one of the largest telephone surveys in the nation and its data are considered the gold standard for public health surveillance on immunization rates. The NIS consists of an interview conducted by telephone with households randomly selected and screened for the presence of young children. Respondents are asked a series of questions about the vaccinations received by selected children (including recommended seasonal flu vaccines), as well as questions about the availability of health insurance and selected demographic information. Respondents are also asked for permission to contact the children’s health providers for the sole purpose of obtaining immunization records, providing an important supplement to the household report. NORC then sends an Immunization History Questionnaire via mail to these health providers – many of whom have previously participated in the NIS over the years and respond at exceptionally high rates.
NORC produces estimates of coverage for all childhood vaccinations recommended by the CDC’s Advisory Committee on Immunization Practices (ACIP). Estimates are produced for the nation as well as for specific areas of the country, including the 50 states, the District of Columbia, the U.S. Virgin Islands, Puerto Rico, Guam, and selected urban areas. These data are used by the CDC and state and local public health agencies to monitor the potential for disease outbreaks at the community level and to allocate resources for the Vaccines for Children (VFC) Program, which ensures that all children in the U.S. have access to vaccinations regardless of financial status.
In recent years, research related to adolescents and the implications of vaccinations on their health has intensified. In response to the need for improved surveillance on teen immunization rates, CDC expanded the use of the NIS sampling frame in 2008 to screen households for the presence of teens between 13-17 years of age. NORC administers an interview comparable to the traditional NIS, including a request for permission to obtain immunization records from the teen’s health providers. NORC provides additional support to CDC in the form of a series of Rapid Flu Surveys, conducted at key points in the flu season and producing real-time estimates on the rate at which the population is receiving recommended flu shots.
Additionally, the NIS sampling frame has provided support for other key surveys via the State and Local Area Integrated Telephone Surveys (SLAITS) mechanism, sponsored by the National Center for Health Statistics (NCHS), including the National Survey of Children’s Health, the National Survey of Children with Special Health Care Needs, the National Survey of Adoptive Parents, the Survey of Adult Transition and Health.
Advances in Survey Research
NIS provides an opportunity to work at the forefront of issues relating to the manner in which research is conducted by telephone: indeed, the traditional household telephone is rapidly being supplemented – and in many cases, replaced – by cell telephones. This new telephony environment poses methodological challenges to researchers as they strive to conduct statistically sound surveys that fully represent the U.S. population. In collaboration with CDC, NORC has spearheaded an ambitious research program to identify best practices for sampling landline and cell telephones and develop valid statistical approaches for weighting and estimation. CDC and NORC also have conducted ongoing analysis on data from the NIS, the National Health Interview Survey (NHIS), and state-based Immunization Information Systems (IIS) to evaluate variance in estimation of immunization rates. The NIS and its companion surveys together provide a valuable mechanism for testing these new approaches and contributing to advances in survey research.