Statistics and Surveillance:
Questions & Answers about Immunization Coverage in the U.S.
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Why measure vaccination coverage?
Data on vaccination coverage is used to identify groups at risk of vaccine-preventable diseases, to provide feedback coverage in an effort to increase coverage, and to evaluate the effectiveness of programs designed to increase coverage.
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What is the purpose of the NIS?
The NIS was established to provide an on-going, consistent data set for analyzing vaccination levels among young children in the US and disseminating this information to interested public health partners. The NIS provides national and state estimates of vaccination coverage-including new vaccines as they are licensed and recommended for use. It also helps us track progress towards Healthy People goals.
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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 the vaccines-with dates-that appear on the child's "shot card" kept in the home, and we also collect 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 verify each child's vaccinations.
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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 rates among different groups, for instance, by income level, race, education level of mothers, and other factors.
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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?
Remember, 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 30,000 children-it is just one of many possible samples. A different sample would result in a different-but probably quite similar-estimate. The drop could be due to chance.
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What are the vaccination coverage estimates for my local area?
The NIS estimates vaccination coverage for the 50 states and 28 selected urban areas
. Due to sampling methods and sample size constraints of the NIS, coverage for smaller geographical areas can not be estimated.
Content last reviewed on October 25, 2006
Content Source: National Center for Immunization and Respiratory Diseases