The National Immunization Survey (NIS) was a large-scale, random-digit-dialed telephone survey, conducted by Abt Global between 1994 and 2005.  Each quarter the survey created rolling annualized estimates of vaccination coverage for children aged 19 to 35 months in the 50 states and in 28 metropolitan areas of the U.S.  National estimates were also created and were published twice a year in the CDC's Morbidity and Mortality Weekly Report.  For the NIS Abt Global staff developed a new sample for each quarter of the calendar year, taking into account the sample characteristics of each state or metropolitan area and sample performance during the calendar year. Each year, approximately 1 million households were screened, and immunization interviews were conducted with approximately 31,500 households containing children between 19 and 35 months of age.  With the permission of the household, medical providers were contacted to collect immunization histories for approximately 22,000 sample children per year.  Final immunization coverage estimates were based on data from these providers. Interviews were conducted in English and Spanish using bilingual interviewers.  Each year approximately 300 interviews were conducted in more than 100 other languages through the Language Line Service.  The NIS also released annual public-use files.