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Questions and Answers About Vaccination Coverage in the U.S.

Questions answered on this page:
  1. Why measure vaccination coverage?

    Data on vaccination coverage are used to identify groups at risk of vaccine-preventable diseases, to monitor progress toward coverage targets, provide feedback coverage in an effort to increase coverage, and to evaluate the effectiveness of programs designed to increase coverage.

  2. What is the purpose of the NIS?

    The NIS was established to provide on-going, consistent data set for analyzing vaccination levels among young children in the US using the same methodology to monitor trends over time. The NIS provides national and state estimates of vaccination coverage and includes new vaccines as they are licensed and recommended for use. It also helps us track progress towards Healthy People goals.

  3. How are data for the NIS collected?

    We use random-digit-dialing to find households with children aged 19 to 35 months. We ask parents or guardians to tell us demographic and socioeconomic information. At the end of the interview, we ask for permission to contact the child's vaccination providers. Providers are then contacted by mail to provide each child's vaccination history.

  4. What are the strengths of NIS?

    The NIS uses a nationally representative sample and provides estimates of coverage that are weighted to represent the entire population - nationally and by region, state, and selected large metro areas. The large sample size allows us to stratify (that is, subdivide) the data so that we can examine vaccination coverage among different groups, for instance, by income level, race, education level of mothers, and other factors.

  5. My state's coverage level is lower than last year, but our vaccination program is strong and we did not expect a drop. How should we interpret this information?

    NIS provides estimates that include a margin of error. That's because it is a sample survey. Even though the sample is quite large-about 15,000 children with adequate provider data-it does not include all children aged 19 to 35 months and is just one of many possible samples. The vaccination coverage estimate that we calculate from the sample might not be exactly the same as the one we would find if we knew the vaccination history of all U.S. children. Since different samples might give slightly different results, an observed decrease in coverage could be due to chance.

  6. What are the vaccination coverage estimates for my local area?

    The NIS estimates vaccination coverage for the 50 states, six urban areas that receive federal immunization grant funding (Chicago, IL; Houston, TX; New York City, NY; Philadelphia, PA; San Antonio, TX; Washington, D.C.), and other selected city and county areas designated by state immunization programs. Due to sampling methods and sample size constraints of the NIS, coverage for smaller geographical areas cannot be estimated.

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