Current Trends Vaccination Coverage of 2-Year-Old Children -- United States, 1993

The primary goal of the Childhood Immunization Initiative (CII) is to increase, by 1996, vaccination levels for 2-year-old children to at least 90% for the most critical doses in the vaccination series (i.e., one dose of measles-mumps-rubella vaccine {MMR} and at least three doses each of diphtheria and tetanus toxoids and pertussis vaccine {DTP}, oral poliovirus vaccine, and Haemophilus influenzae type b vaccine {Hib}) and to at least 70% for three or more doses of hepatitis B (Hep B) vaccine (1). This report presents estimates, based on the National Health Interview Survey (NHIS), of the annual national vaccination coverage levels for children aged 19-35 months (median: 27 months) for 1993, compares estimates for 1993 with those for 1992, and compares estimates for the first 6 months of 1993 with third and fourth quarter 1993 estimates.

To monitor vaccination coverage, national estimates of vaccination levels for 2-year-old children are derived from the NHIS, a cross-sectional household interview survey of the civilian, noninstitutional population of the 50 states and the District of Columbia (2). The NHIS is the primary survey methodology through which progress is monitored toward reaching the CII goal. In-person interviews with an adult respondent are conducted each week throughout the year. Data on vaccinations are collected through a special Immunization Supplement questionnaire for children aged less than 6 years; vaccination information is obtained from vaccination records (if available) or parental recall. Sample sizes for annual estimates permit analysis of vaccination status by poverty * classification, place of residence, and race to assist in targeting vaccination activities. Limitations in sample size precluded analysis of data by ethnicity and by individual races other than black and white. Confidence intervals (CIs) were calculated using the Software for Survey Data Analysis (SUDAAN) (3).

During 1993, vaccination coverage rates ranged from 16.3% for three or more doses of Hep B to 88.2% for three or more doses of DTP (Table_1). Coverage was 67.1% for the combined series of four doses of DTP, three doses of polio vaccine, and one dose of MMR (4:3:1 series).

When compared with 1992, vaccination coverage rates for 1993 for each individual vaccine, except for measles-containing vaccine, and for each combined series were higher; vaccine-specific increases ranged from 1.6 to 26.8 percentage points. Increases were greatest for three or more doses of Hib (from 28.2% {95% CI=25.6%- 30.9%} to 55.0% {95% CI=52.3%-57.7%}), four or more doses of DTP (from 59.0% {95% CI=56.1%-61.9%} to 72.1% {95% CI=69.4%-74.8%}), and the 4:3:1 combined series (from 55.3% {95% CI=52.5%-58.1%} to 67.1% {95% CI=64.3%-69.9%}).

In 1993, coverage rates were lower for children below the poverty level than for children at or above the poverty level for each individual vaccine and for each combined series (Table_2). The difference ranged from 6.9 (three or more doses of Hep B) to 15.6 percentage points (three or more doses of Hib) and was statistically significant for all but one category (three or more doses of polio).

In 1993, race-specific vaccination coverage rates were similar for all vaccine categories except measles-containing vaccine (Table_2). For this category, rates were lower among black children and children of other races.

In 1993, coverage rates for three or more doses of Hep B were lower among children living in rural areas ** than among children in suburban areas (Table_2). For three or more doses of Hib, coverage rates were lower among children living in urban areas than children in suburban areas.

When comparing rates during 1993, vaccine coverage increased for three or more doses of Hib (Table_3), but the trend was stable for other vaccines. Coverage rates for the 4:3:1 series decreased from 71.6% in the third quarter to 66.4% in the fourth quarter, although the difference was not statistically significant. Reported by: National Immunization Program; Div of Health Interview Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: The vaccination coverage estimates for 1993 are the highest coverage rates ever reported for a given year for children aged 19-35 months in the United States and indicate progress toward the CII goals for 1996. However, up to 2 million U.S. children remain in need of one or more doses of the recommended vaccines, and coverage levels remain low for three doses of Hib and three or more doses of Hep B vaccine. In addition, the level of coverage for measles-containing vaccine in 1993 suggests that the heightened vaccination efforts that followed the measles epidemic of 1989-91 may have stabilized. Understanding the differences in vaccination coverage rates in relation to poverty level also will assist in targeting population groups with lower coverage levels.

Findings in this report that indicate vaccination coverage rates vary by race may reflect differences in factors such as socioeconomic status, access to medical care, prevalence of specific risks, or misclassification of race. Further clarification of these factors should assist in targeting vaccination coverage programs and activities.

To monitor progress in reaching the vaccination coverage goals of the CII, vaccination levels will be reported quarterly. However, such data should be interpreted with caution; the larger number of children in the annual samples provides greater precision for those estimates than the quarterly samples. For example, the decrease in 4:3:1 coverage from the third to the fourth quarter may represent chance variation rather than a real decline in coverage.

The five strategies of CII are to 1) improve the delivery of vaccines; 2) reduce the cost of vaccines for parents; 3) enhance awareness, partnerships, and community participation; 4) monitor coverage and disease; and 5) improve vaccines and their use. Parents, health-care providers, government officials, and private-sector partners will need to refine strategies and intensify efforts to fully implement and achieve these goals.

References

1. CDC. Reported vaccine-preventable diseases -- United States, 1993, and the Childhood Immunization Initiative. MMWR 1994;43:57-60.

2. Massey JT, Moore TF, Parsons VL, et al. Design and estimation for the National Health Interview Survey, 1985-94. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1989. (Vital and health statistics; series 2, no. 110).

3. Shah BV. Software for Survey Data Analysis (SUDAAN) version 5.5 {Software documentation}. Research Triangle Park, North Carolina: Research Triangle Institute, 1991.

* Poverty statistics are based on definitions developed by the Social Security Administration that include a set of income thresholds that vary by family size and composition. 

** Rural areas were those not in a metropolitan statistical area (MSA); suburban areas were those in an MSA but outside the central city; and urban areas were the central city of an MSA.

Table_1
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TABLE 1. Vaccination levels among children aged 19-35 months, by selected vaccines
-- United States, 1992 and 1993
=====================================================================================
                               1992                    1993
                         -----------------      ------------------
Vaccine                  %     (95% CI *)          %   (95% CI)
------------------------------------------------------------------
DTP/DT +
  >=3 doses              83.0  (80.8-85.2)       88.2  (86.5-89.9)
  >=4 doses              59.0  (56.1-61.9)       72.1  (69.4-74.8)

Poliovirus
  >=3 doses              72.4  (70.1-74.7)       78.9  (76.2-81.6)

Haemophilus influenzae
  type b
  >=3 doses              28.2  (25.6-30.9)       55.0  (52.3-57.7)

Measles-containing       82.5  (80.2-84.8)       84.1  (81.9-86.3)

Hepatitis B
  >=3 doses              ---        ---          16.3  (14.0-18.6)

3 DTP/3 polio/1 MMR &    68.7  (66.2-71.2)       74.5  (71.9-77.1)

4 DTP/3 polio/1 MMR @    55.3  (52.5-58.1)       67.1  (64.3-69.9)
------------------------------------------------------------------
* Confidence interval.
+ Diphtheria and tetanus toxoids and pertussis vaccine/Diphtheria and
  tetanus toxoids.
& Three doses of DTP, three doses of poliovirus, and one dose of
  measles-mumps-rubella vaccine.
@ Four doses of DTP, three doses of poliovirus, and one dose of
  measles-mumps-rubella vaccine.
=======================================================================

TABLE 2. Vaccination levels for routinely recommended vaccines among children aged 19-35 months, by selected characteristics -- United States, 1993
==============================================================================================================================================================
                                                   Individual vaccine
                    -----------------------------------------------------------------------------------------------------            Combined series
                                                       >=3 Doses                         Measles-             >=3 Doses        -------------------------------
                    >=3 Doses DTP *   >=4 Doses DTP    poliovirus       >=3 Doses Hib +  containing           hepatitis B      4:3:1 &          3:3:1 @
                    ---------------   -------------    ------------     ---------------  --------------       ------------     ------------     --------------
Characteristic      %   (95% CI **)   %   (95% CI)     %   (95% CI)     %   (95% CI)     %     (95% CI)       %   (95% CI)     %   (95% CI)     %   (95% CI)
--------------------------------------------------------------------------------------------------------------------------------------------------------------
Socioeconomic
  status
  Below poverty ++
    level          80.6 (+/- 5.2)     65.3 (+/- 6.4)   73.3 (+/- 6.2)   44.0 (+/- 5.9)   78.4   (+/- 5.0)     11.3  (+/- 3.9)  58.7 (+/- 6.7)   66.8 (+/- 6.5)
  At or above
    poverty level  90.8 (+/- 1.8)     74.6 (+/- 2.8)   81.0 (+/- 2.6)   59.6 (+/- 3.1)   87.0   (+/- 2.4)     18.2  (+/- 2.6)  70.5 (+/- 2.8)   77.7 (+/- 2.6)

Race
  White            89.4 (+/- 2.0)     73.0 (+/- 3.2)   79.8 (+/- 3.1)   57.0 (+/- 3.2)   86.0   (+/- 2.3)     16.3  (+/- 2.6)  68.4 (+/- 3.2)   75.7 (+/- 3.0)
  Black            82.6 (+/- 5.1)     69.2 (+/- 6.5)   73.4 (+/- 6.0)   44.8 (+/- 6.5)   76.9   (+/- 5.8)     16.0  (+/- 4.9)  61.8 (+/- 7.1)   69.2 (+/- 6.6)
  Other &&         84.5 (+/-13.0)     64.7 (+/-16.0)   80.8 (+/-13.0)   56.9 (+/-16.0)   72.5   (+/-16.4)     16.7  (+/-10.5)  58.4 (+/-17.1)   68.0 (+/-17.3)

Residence @@
  Urban            85.8 (+/- 3.1)     68.5 (+/- 4.9)   75.3 (+/- 4.0)   47.8 (+/- 5.0)   84.2   (+/- 3.9)     17.4  (+/- 4.0)  62.1 (+/- 5.3)   71.5 (+/- 4.4)
  Suburban         89.8 (+/- 2.6)     75.6 (+/- 4.1)   79.7 (+/- 4.0)   60.5 (+/- 4.3)   86.2   (+/- 2.8)     19.0  (+/- 3.2)  71.4 (+/- 4.2)   76.3 (+/- 4.1)
  Rural            88.5 (+/- 3.8)     70.6 (+/- 5.4)   82.5 (+/- 5.1)   55.2 (+/- 5.7)   79.8   (+/- 5.3)      9.3  (+/- 4.3)  66.0 (+/- 5.6)   75.3 (+/- 5.6)

Total              88.2 (+/- 1.7)     72.1 (+/- 2.7)   78.9 (+/- 2.7)   55.0 (+/- 2.7)   84.1   (+/- 2.2)     16.3  (+/- 2.3)  67.1 (+/- 2.8)   74.5 (+/- 2.6)
--------------------------------------------------------------------------------------------------------------------------------------------------------------
 * Diphtheria and tetanus toxoids and pertussis vaccine.
 + Haemophilus influenzae type b vaccine.
 & Four doses of DTP, three doses of poliovirus, and one dose of measles-mumps-rubella vaccine.
 @ Three doses of DTP, three doses of poliovirus, and one dose of measles-mumps-rubella vaccine.
** Confidence interval.
++ Poverty statistics are based on definitions developed by the Social Security Administration that include a set of income thresholds that vary
   by family size and composition.
&& Limitations in sample size precluded collection of data about ethnicity and analysis of data for races other than black and white.
@@ Rural areas were those not in a metropolitan statistical area (MSA); suburban areas were those in an MSA but outside the central city; and
   urban areas were the central city of an MSA.
==============================================================================================================================================================

TABLE 3. Vaccination levels among children aged 19-35 months, by selected vaccines
-- United States, January-June and third and fourth quarters, 1993
========================================================================================
                          January-June          July-September        October-December
                          -----------------     ----------------      ------------------
Vaccine                   %     (95% CI *)      %      (95% CI)       %       (95% CI)
----------------------------------------------------------------------------------------
DTP/DT +
  >=3 doses               87.2  (84.3-90.4)     89.9  (86.9-93.0)     88.1   (84.6-91.5)
  >=4 doses               71.1  (67.1-75.1)     74.8  (69.9-79.7)     71.6   (66.4-76.7)

Poliovirus
  >=3 doses               78.4  (74.8-82.0)     80.4  (75.8-84.9)     78.5   (73.9-83.0)

Haemophilus
  influenzae
  type b
  >=3 doses               49.6  (45.4-53.8)     60.3  (55.0-65.7)     58.3   (53.1-63.5)

Measles-
  containing              80.8  (77.2-84.4)     85.9  (82.0-89.8)     86.9   (83.3-90.5)

Hepatitis B
  >=3 doses               12.7  ( 9.4-16.0)     15.7  (12.1-19.2)     22.5   (17.8-27.1)

3 DTP/3 polio/1 MMR &     72.0  (68.1-75.9)     78.7  (74.2-83.2)     74.3   (69.4-79.2)

4 DTP/3 polio/1 MMR @     64.8  (60.6-68.9)     71.6  (66.7-76.4)     66.4   (61.1-71.7)
-----------------------------------------------------------------------------------------
* Confidence Interval.
+ Diphtheria and tetanus toxoids and pertussis vaccine/diphtheria and tetanus toxoids.
& Three doses of DTP, three doses of poliovirus, and one dose of measles-mumps-rubella
  vaccine.
@ Four doses of DTP, three doses of poliovirus, and one dose of measles-mumps-rubella
  vaccine.
=========================================================================================

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