and Statistics > Immunization Coverage in
(National Immunization Survey)
(frequently asked questions)
measure vaccination coverage?
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.
- 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.
- 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.
- 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.
- 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
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.
- 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.