Vaccination Coverage of 2-Year-Old Children -- United States, 1991-1992

Protecting children against vaccine-preventable diseases is a national priority in public health. Because approximately 80% of childhood vaccine doses are recommended for administration during the first 2 years of life, vaccination coverage among children must be continuously monitored. National estimates of vaccination coverage were calculated annually from 1959 through 1985 but not for 1986-1990. Beginning in 1991, national estimates of vaccination coverage of preschool children have been available through the National Health Interview Survey (NHIS), a national survey of the civilian noninstitutionalized population conducted by CDC's National Center for Health Statistics (1). This report presents 1992 national estimates of vaccination coverage for 2-year-old children and describes changes from 1991 to 1992.

The NHIS collects vaccination information during household interviews. If vaccination records are available, data are abstracted from the record. If such records are not available, information is based on parental recall. For data measurement, 2-year-old children are defined as persons aged 19-35 months. The proportion of children vaccinated were separately analyzed by poverty classification and place of residence. In addition, to assist in targeting vaccination activities based on cultural differences, data were analyzed by race. Limitations in sample size precluded collection of data on ethnicity and analysis of data for races other than black and white.

Coverage for measles-containing vaccine was similar in 1991 and 1992 (82.0% and 82.5%, respectively) (Table_1). In contrast, coverage in 1992 was substantially higher than that in 1991 for diphtheria and tetanus toxoids and pertussis vaccine (DTP) and poliovirus vaccine. From 1991 to 1992, coverage for three or more doses of DTP increased from 68.8% to 83.0% and for three or more doses of poliovirus vaccine, from 53.2% to 72.4%.

Children living below the poverty level* were less well vaccinated than others. Differences between children living below the poverty level and those living at or above the poverty level ranged from a low of 4.1 percentage points for measles (80.2% vs 84.3%) to a high of 8.1 percentage points for polio (66.6% vs 74.7%). Vaccination levels in urban, suburban, and rural areas were similar in 1992. In general, vaccination levels were lower in black children than in white.

In 1992, 71%-72% of children at or above the poverty level were in need of at least one vaccine (Table_2). Among white children, 72%-75% were in need of at least one of the recommended vaccines. Overall, an estimated 1 million 2-year-olds required a single dose of measles-containing vaccine, and 1.6 million 2-year-olds required one or more doses of poliovirus vaccine. Approximately 1 million children had not received at least three doses of DTP vaccine. Reported by: National Immunization Program; Div of Health Interview Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: The findings in this report summarizing NHIS data document the overall continuing problem of undervaccination of children in the United States. However, vaccination coverage for some antigens has improved in some age groups -- particularly for vaccination against measles in the preschool population. Estimated measles vaccine coverage for 2-year-olds in 1985 was 61%, compared with 82% in 1991 and 1992; before 1991, the highest previously documented level was 67% in 1982 (CDC, unpublished data, 1993). The recent increase in coverage reflects the national response to increased vaccination levels following the measles resurgence during 1988-1991; as a result of these efforts, the incidence of measles decreased to a historic low in 1993 (2).

This report also documents a substantial increase in poliovirus and DTP vaccination levels from 1991 to 1992. At least two factors may account for these increases. First, many state and local public health agencies, in collaboration with national and local private voluntary organizations, have intensified their efforts to vaccinate preschool children, especially since the 1989- 1991 measles resurgence. Second, changes in survey methodology between 1991 and 1992 have simplified data collection from parental recall. In 1991, respondents were required to specify the exact ages at which vaccinations were administered for the full number of doses to be credited; however, some parents had difficulty recalling the exact ages at which their child received vaccinations. As a consequence, in 1992, a parental response that the child had received all doses of a particular antigen was accepted; retrospective studies have shown this methodology has enhanced the accuracy of data (CDC, unpublished data, 1993). Because of difficulties in determining vaccination status from parental recall (3), in 1994, the NHIS will include a check of provider records for all children aged 19-35 months, thus allowing for adjustment of overall survey results. In addition, health-care providers will encourage parents to maintain home vaccination records (4).

Despite ongoing and substantial efforts to improve the vaccine delivery system in the United States, vaccination levels for 2-year-olds remain below 90%. In addition, coverage varies by and are substantially lower in some population groups, especially those underserved by the health-care system.

Differences in vaccination levels among racial/ethnic groups may be influenced by social and cultural phenomena and require special interventions. For example, during 1992 in Los Angeles, 42% of Hispanic preschool children were fully vaccinated by age 24 months, compared with 25% of black children, even though Hispanic parents reported lower mean annual family incomes ($3218 vs. $4596) and lower mean years of education (8.6 years vs. 12.5 years) (CDC, unpublished data, 1993).

Limitations in the sample size of the 1992 NHIS preclude estimation of vaccination coverage of Hispanic populations; however, the increased incidence of measles among Hispanics before and during the measles resurgence suggests that overall vaccination coverage is also substantially lower in Hispanics than in white non-Hispanics (5-7 ). The prevention of vaccine-preventable diseases in the United States will require that uniformly high vaccination levels for preschool children be achieved and sustained in all communities.

References

1. 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).

2. CDC. Measles -- United States, first 26 weeks, 1993. MMWR 1993;42:813-6.

3. Goldstein KP, Kviz FJ, Daum RS. Accuracy of immunization histories provided by adults accompanying preschool children to a pediatric emergency department. JAMA 1993;270:2190-4.

4. CDC. Standards for Pediatric Immunization Practices {Standard 9}, 1993:15.

5. Orenstein WA, Atkinson W, Mason D, Bernier RH. Barriers to vaccinating preschool children. J Health Care Poor Underserved 1990;1:315-30.

6. CDC. Measles vaccination levels among selected groups of preschool-aged children -- United States. MMWR 1991;40:36-9.

7. Gindler JS, Atkinson WL, Markowitz LE, Hutchins SS. Epidemiology of measles in the United States in 1989 and 1990. Pediatr Infect Dis J 1992;11:841-6.

• 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.

+------------------------------------------------------------------- ------+ | Erratum: Vol. 42, Nos. 51 & 52 | |             | | SOURCE: MMWR 43(1);18 DATE: Jan. 14, 1994 | |             | | In the article "Vaccination Coverage of 2-Year-Old Children -- | | United States, 1991-1992," on page 986, the first two sentences of | | the second paragraph should read "In 1992, 71%-72% of children in | | need of at least one of the recommended vaccines were at or above | | the poverty level (Table_2). Among children in need of at least one | | of the recommended vaccines, 72%-75% were white." In addition, in | | Table_1, the plus or minus symbol should appear in front of each | | 95% confidence interval variable. | |             | +------------------------------------------------------------------- ------+
Table_1
Note: To print large tables and graphs users may have to change their printer settings to landscape and use a small font size.

TABLE 1. Percentage * of 2-year-olds + receiving doses of diphtheria and tetanus toxoids
and pertussis vaccine (DTP), poliovirus vaccine, and measles-containing vaccine (MCV),
by selected characteristics -- United States, 1991 and 1992
======================================================================================================================
                          >=3 doses DTP                  >=3 doses poliovirus                   1 dose MCV
                  ------------------------------    ------------------------------    ------------------------------
Characteristic    1991 (95% CI &)  1992 (95% CI)    1991 (95% CI)    1992 (95% CI)    1991 (95% CI)    1992 (95% CI)
--------------------------------------------------------------------------------------------------------------------
Socioeconomic
 status @
  Below poverty
   level          53.0  ( 8.8)     79.7   (5.7)     38.7  ( 7.9)     66.6   (6.2)     73.4  ( 6.8)     80.2  ( 5.6)
  At or above
   poverty level  75.7  ( 2.8)     84.6   (2.2)     59.5  ( 3.6)     74.7   (2.5)     86.6  ( 2.3)     84.3  ( 2.2)

Race
  White           73.4  ( 3.6)     84.8   (2.3)     57.3  ( 4.0)     74.1   (2.6)     82.9  ( 2.7)     83.6  ( 2.4)
  Black           50.6  ( 7.3)     74.7   (6.3)     35.6  ( 6.1)     62.7   (7.0)     77.4  ( 7.3)     77.9  ( 6.3)
  Other **        58.0  (12.5)     79.3   (9.0)     49.8  (14.8)     75.5   (9.9)     83.8  (12.5)     79.9  (10.0)

Residence
  Urban           64.8  ( 4.4)     82.5   (3.5)     49.9  ( 4.7)     74.1   (4.0)     78.4  ( 4.0)     84.5  ( 2.7)
  Suburban        72.3  ( 4.3)     84.4   (2.8)     55.8  ( 5.2)     72.6   (3.4)     85.0  ( 3.5)     83.3  ( 3.1)
  Rural           67.6  ( 6.0)     80.7   (5.4)     52.5  ( 5.9)     69.0   (5.3)     81.1  ( 5.7)     77.2  ( 6.7)

Total             68.8  ( 3.0)     83.0   (2.2)     53.2  ( 3.4)     72.4   (2.3)     82.0  ( 2.5)     82.5  ( 2.3)
--------------------------------------------------------------------------------------------------------------------
 * Data are based on household interviews of a sample of the civilian noninstitutionalized
 population. Refusals and unknowns were excluded (DTP: 4% in 1991, 16% in 1992;
 measles-containing vaccine: 3% in 1991, 14% in 1992; poliovirus vaccine: 3% in 1991, 17% in
 1992). In 1991, 45.6% of respondents had a vaccination record; in 1992, 31.2% had a vaccination
 record.
 + Children aged 19-35 months.
 & 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.
** Data for American Indians/Alaskan Natives and Asians/Pacific Islanders were combined
 because of limitations in sample size.
======================================================================================================================

TABLE 2. Percentage of all undervaccinated 2-year-olds * requiring at least one dose
of diphtheria and tetanus toxoids and pertussis vaccine (DTP), poliovirus vaccine,
and/or measles-containing vaccine (MCV), by selected characteristics -- United
States, 1992
===============================================================================================
 Characteristic            <3 doses DTP    <3 doses poliovirus     0 doses MCV
--------------------------------------------------------------------------------
 Socioeconomic status +
   Below poverty level          28                  29                  28
   At or above
    poverty level               72                  71                  72
 Total                         100                 100                 100

 Race
   White                        72                  75                  75
   Black                        22                  20                  19
   Other &                       6                   4                   6
 Total                         100                  99                 100
--------------------------------------------------------------------------------
* Children aged 19-35 months.
* 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.
& Data for American Indians/Alaskan Natives and Asians/Pacific Islanders were combined
  because of limitations in sample size.
===============================================================================================

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