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Each annual birth cohort in the United States comprises approximately
four million infants. Maintaining the gains in childhood vaccination coverage
attained during the 1990s among these children poses an ongoing challenge
for public health. The National Immunization Survey (NIS) is an ongoing survey
that provides estimates of vaccination coverage among children aged 19-35
months on the basis of data for the most recent 12 months for each of the
50 states and 28 selected urban areas. This report presents NIS findings for
2001,* which indicate a substantial nationwide increase in coverage with ≥1
dose of varicella vaccine (VAR), generally steady coverage for other vaccines
nationwide, and wide variability in coverage among the states and urban areas
covered by NIS.
To collect vaccination data for all age-eligible children, NIS uses
a quarterly random-digit–dialing sample of telephone numbers for each
survey area. NIS methodology, including how the responses are weighted to
represent the population of children aged 19-35 months, has been described
previously.1,2 During 2001,
household interviews were completed for 33,437 children; of these, adequate
health-care provider information was available for 23,551. The response rate
for eligible households for the 78 survey areas was 63.8%. For this report,
NIS data for 2001 were compared with data for 2000.†3
National vaccination coverage with ≥1 dose of VAR increased from
67.8% (95% confidence interval [CI] = ± 0.9%) in 2000 to 76.3% (95%
CI = ± 0.8%) in 2001. Coverage with ≥1 dose of measles, mumps, and
rubella (MMR) vaccine increased from 90.5% (95% CI = ± 0.6%) in 2000
to 91.4% (95% CI = ± 0.6%) in 2001, and coverage with ≥3 doses of
hepatitis B vaccine (HepB) decreased from 90.3% (95% CI = ± 0.6%) in
2000 to 88.9% (95% CI = ± 0.7%) in 2001.
In 2001, estimated vaccination coverage differed substantially among
states. The estimated coverage with the 4:3:1:3:3 series‡ ranged from
81.7% in Rhode Island to 63.2% in New Mexico, a difference of 18.5 percentage
points. Variability among states was lowest for 3 doses of diphtheria and
tetanus toxoids and pertussis vaccine, diphtheria and tetanus toxoids, and
diphtheria and tetanus toxoids and acellular pertussis vaccine (DTP/DT/DTaP)
(9.1 percentage points; range: 89.2%-98.3%) and highest for 1 dose of VAR
(34.1 percentage points; range: 55.8%-89.9%). Variability among the 28 urban
areas was slightly greater than among states. Among the 28 urban areas, the
highest estimate for coverage with the 4:3:1:3:3 series was 79.5% in Jefferson
County, Alabama, and the lowest was 57.7% in Detroit, Michigan, a difference
of 21.8 percentage points.
For the 4:3:1:3:3 series, the magnitude of the disparity between the
highest and lowest estimates for states has been consistent during the preceding
4 years (20.3 percentage points in 1998, 21.4 in 1999, 19.3 in 2000, and 18.5
in 2001) having decreased from 28.1 percentage points in 1997. The decreased
disparity in 1998 compared with 1997 was attributed mostly to more complete
implementation of hepatitis B vaccination in a few states. No state consistently
had either the highest or lowest coverage estimates from year to year.
L Barker, PhD, E Luman, MS, Z Zhao, PhD, P Smith, PhD, R Linkins, PhD,
Data Management Div; J Santoli, MD, L Rodewald, MD, Immunization Svcs Div;
M McCauley, MTSC, Office of the Director, National Immunization Program, CDC.
The findings in this report indicate that among U.S. children aged 19-35
months, coverage with recommended vaccines remains near all-time highs, and
declines observed recently probably are too limited to pose a major public
health risk. Although coverage with recommended vaccines for each new birth
cohort remains high, vigilance is needed to maintain these high levels. Eliminating
the disparity between states and urban areas with the highest and lowest coverage
remains a priority. Should vaccine-preventable disease be introduced in an
area with low coverage, groups of susceptible persons might serve as a reservoir
to transmit disease.
The findings in this report are subject to at least three limitations.
First, NIS is a telephone survey; although statistical weights adjust for
nonresponses and households without telephones, some bias might remain. Second,
NIS relies on provider-verified vaccination histories; incomplete records
and reporting could result in underestimates of coverage. The estimation procedure
assumes that coverage among children whose providers do not respond is similar
to that among children whose providers respond. Finally, although national
level estimates are precise, estimates for states and urban areas should be
interpreted with caution.4
In October 2000, the Advisory Committee on Immunization Practices recommended
that all children aged 2-24 months without contraindications receive 4 doses
of pneumococcal vaccine.5 The first NIS
coverage estimates will be presented next year because the recommendation
applies to all children covered by the 2002 NIS.
Shortages of routinely recommended childhood vaccines, including DTaP,
pneumococcal conjugate vaccine (PCV7), MMR, varicella vaccine, and tetanus
toxoid began in early 2001.6-9 The
shortages did not affect coverage in 2001 because almost all children included
in the 2001 NIS were eligible to receive recommended vaccines before 2001.
As children potentially affected by the shortages are surveyed by NIS, CDC
will monitor the impact on coverage. The supplies of all vaccines, except
PCV7, have improved. Additional information about the status of the vaccine
shortages is available at http://www.cdc.gov/nip/news/shortages/default.htm.
*For the January-December 2001 reporting period, NIS included children
born during February 1998–May 2000.
†For the January-December 2001 reporting period, NIS included
children born during February 1997–May 1999.
‡Comprises ≥4 doses of diphtheria and tetanus toxoids and
pertussis vaccine, diphtheria and tetanus toxoids, and diphtheria and tetanus
toxoids and acellular pertussis vaccine; ≥3 doses of poliovirus vaccine;
≥1 dose of measles-containing vaccine; ≥3 doses of Haemophilus influenzae type b vaccine; and ≥3 doses of HepB vaccine.
National, State, and Urban Area Vaccination Coverage Levels Among Children Aged 19-35 Months—United States, 2001. JAMA. 2002;288(14):1713–1714. doi:10.1001/jama.288.14.1713