Data Management Statistics

National Immunization Survey

What is the NIS?
Since 1994, the National Immunization Survey (NIS) collects information on the immunization coverage of children 19 months to 35 months of age across the United States. Data are used to monitor immunization coverage in the preschool population in 78 non-overlapping geographic areas. The survey is a collaborative effort between the National Center of Health Statistics and the Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases. More information regarding the NIS can be found at www.cdc.gov/nis.

Summary of NIS Data
Click here for a pdf summary of the Virginia and National rates.

What is a 95% Confidence Interval (CI)?
A 95% confidence interval is a concept from random sampling theory where an estimate of the coverage rate in a large population is produced from the rate found in a randomly picked group of children who are part of the large group. The confidence interval indicates that if the survey were repeated over and over, 95% of the surveys would produce a coverage estimate that fell within the range of the 95% confidence interval. For example, a rate of 75% +/- 2% has a confidence interval of 2%. This means that the estimated coverage rate is actually between 73% and 77%.

How accurate and reliable are these numbers?
The NIS is accurate and reliable. The accuracy is supported by the agreement between the NIS, a telephone survey, and the National Health Interview Survey, a nationally representative, household, door-to-door survey. The reliability of the NIS is reflected in the size of the confidence interval; it is more reliable at the national level than at the state or urban level. This is because the number of interviews overall is so much larger than the number of interviews for any state.

Why do the NIS vaccination rates differ from other methods such as CASA, registries, and HEDIS?
There are many possible reasons why the rates could differ, because the systems use:

• different age ranges (19-35 months, 24-35 months);
• different computation rules (all doses, only age-appropriate doses);
• different sampling methods (population vs. provider vs. registry based);
• incomplete records (missing doses given by different providers);
• different vaccine combinations (4-3-1, 4-3-1-3, 4-3-1-1-2 [HEDIS 3.0/1997]).

Using CDC's NIS Web Site to View VA and National Data

1. Click on the link to http://www.cdc.gov/vaccines/stats-surv/imz-coverage.htm
2. Select the appropriate year from the table labeled "NIS Data."
3. From the next screen, select the appropriate file (usually the coverage with individual vaccines and vaccination series by state, Excel or html file).

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