Fifteen Year Analysis of NIS Data

Background: The National Immunization Survey (NIS) has assessed the rates of up-to-date (UTD) immunization coverage in 19- to 35-month old American children since 1994. 

Objectives: To describe changes over the past 15 years of national vaccination data and recommend changes for future vaccination reporting. 

Methods: Analysis of 15 years of NIS data as reported on the CDC.gov/vaccines website.

Results: In 1994, the NIS reported on 3 vaccines (DTP, polio, measles-containing vaccine).  Over 15 years, 4 vaccines have been added to NIS reports for combined rates of vaccination (Hib, hepatitis B, varicella, and pneumococcal conjugate vaccine). Five different combined rates (431; 4313; 43133; 431331; 4313314) have been reported. All combined rates require being up-to-date for every vaccine dosage in every series (“UTD-all-series”).  Averaging methods, better reflecting disease protection, have not been reported, but can be calculated from data provided.  Differences between UTD-all-series and averaging methods show that over the 15 years of the survey, UTD-all-series rates are between 8 and 23% lower than rates derived from complete series averages. The year after a new vaccine is added to the cumulative rate, UTD-all-series rates decreased 6.5%, whereas the disease protection rate rose 0.2%. Vaccine shortages substantially reduce UTD-all-series rates, although averaging rates are less impacted.

Conclusions: The NIS has served as an important program for measuring and reporting on the status of vaccine protection of American children.  NIS reports should provide both UTD-all-series and averaging rates.  Averages for completion of each individual dose cumulatively for all vaccines as well as vaccine series for which no vaccine(s) has been given should also be reported.