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Vaccination Coverage of 2-Year-Old Children -- United States, Third Quarter, 1993

In 1993, the Childhood Immunization Initiative (CII) was instituted to increase vaccination coverage among 2-year-old children to at least 90% by 1996 for four of the five vaccines routinely recommended for children * and to at least 70% for three doses of hepatitis B vaccine (1). To monitor progress toward these goals, national estimates of vaccination coverage are needed. This report presents national estimates of vaccination coverage among 2-year-old children derived from provisional data from the National Health Interview Survey (NHIS) for the third quarter of 1993 and describes the trend in vaccination coverage since 1992, the baseline year.

The NHIS, a probability sample of the civilian, noninstitutionalized U.S. population, provides quarterly data to calculate these national estimates (2). From July through September 1993, the NHIS collected vaccination data from a random sample (n=483) of survey respondents during household interviews. Vaccination records were available for the children of 33.7% of respondents; for 61.1% of respondents, such records were unavailable and data were based on parental recall. Children's vaccination history was obtained from both sources by 4.4% of respondents and was unknown or refused by 0.8%. For data measurement, 2-year-old children were defined as persons aged 19-35 months at the time of the survey. The children for whom data were collected were a mean age of 27 months, were born during August 1990-February 1992, and had ranged in age from 2 to 15 months (the recommended ages for vaccination) sometime during October 1990-May 1993. Data were weighted to provide national estimates. Confidence intervals were calculated using standard errors generated by the Software for Survey Data Analysis (SUDAAN) (3).

Compared with 1992 baseline data from the NHIS, data for the third quarter of 1993 indicate that coverage levels for the individual vaccinations recommended routinely for children and the combined series ** of vaccinations increased among 2-year-olds (Table_1) (4). Coverage with three or more doses of vaccine increased for diphtheria and tetanus toxoids and pertussis vaccine (DTP)/DT (from 83.0% to 89.9%), for polio vaccine (from 72.4% to 80.4%), for Haemophilus influenzae type b vaccine (Hib) (from 28.2% to 60.3%), for any measles-containing vaccine (MCV) (from 82.5% to 85.9%), and for the 4:3:1 combined series (from 55.3% to 71.6%). Baseline data for hepatitis B vaccine were not available. The increases are statistically significant (p less than 0.05) for all vaccines (except MCVs) and the 4:3:1 combined series.

Reported by: Assessment Br, Data Management Div, National Immunization Program; Div of Health Interview Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: The findings in this report document an increasing trend in the level of vaccination coverage in the United States from 1992 through the third quarter of 1993 and demonstrate continuing progress toward the 1996 vaccination coverage goal of the CII. During this period, vaccination levels for DTP, polio vaccine, and MCVs were the highest ever reported among 2-year-olds in the United States. However, these levels remain below the CII's 1996 goal of at least 90% coverage. Specifically, an estimated 500,000 U.S. children aged 19-35 months lack at least three doses of DTP; 1 million need one or more doses of polio vaccine, and 750,000 need one or more doses of an MCV. Overall, only an estimated 72% of children received the complete 4:3:1 combined series; therefore, an estimated 1.5 million children need one or more doses to be fully vaccinated.

The findings in this report are subject to at least one limitation. Because a substantial proportion of the NHIS data was based on parental recall, the data may be subject to recall bias or other reporting errors. Beginning with the 1994 survey, all vaccination histories will be verified by reviewing provider records.

Although vaccination levels increased for Hib from 1992 through the third quarter 1993 and for hepatitis B vaccine through the first three quarters of 1993, coverage with these vaccines remained substantially low compared with levels for DTP, polio, and MCV. Two factors may account for the low level of coverage with three doses of Hib. First, most of the NHIS data in this report were for children who were born after promulgation of the recommendations for universal administration of Hib in October 1990 (5). Because nationwide implementation of recommendations does not occur immediately among providers, the anticipated increase in vaccination coverage levels often occurs several months to several years after implementation. Although universal vaccination with Hib has been fully implemented in the United States, the expected increase in Hib coverage levels will be adequately reflected only in future reports. This report documents an increase of 32 percentage points in Hib coverage from 1992 through third quarter 1993. Second, catch-up of children in need of Hib can be accomplished with fewer than three doses. For example, a 15-month-old child who never received a dose of Hib needs only one dose. One factor may account for the low level of hepatitis B coverage. Most of the NHIS data in this report were for children born before the recommendations for universal hepatitis B vaccination were promulgated in November 1991 (6). Consequently, most of these children did not receive this vaccine when they were the recommended ages for vaccination. To compensate for the time required to fully implement universal vaccination, the 1996 CII vaccination coverage goal for hepatitis B vaccine is 70% rather than 90%.

The reasons for the overall increase in vaccination coverage levels from 1992 through the third quarter of 1993 are unclear. One possible explanation is associated with the recent measles epidemic in the United States during 1989-1991. During and immediately after the epidemic, a substantial number of the children for whom the NHIS data in this report were provided were the recommended ages for routine vaccination. The immediate risk for measles, the heightened awareness that preschool children needed vaccinations, and the media's focus on the severity and complications of vaccine-preventable diseases may have established vaccination as a high priority among parents and providers (7). As a result, parents may have intensified efforts to seek vaccinations for their children and providers may have more consistently sought to vaccinate children at the earliest recommended ages. However, the effects of efforts aimed at increasing vaccination coverage during and/or after an outbreak of vaccine-preventable disease may be temporary.

The substantial number of undervaccinated children in the United States and the possibly temporary increases in vaccination coverage after the recent measles resurgence underscore the importance of fully implementing the CII, which focuses on 1) improving delivery, 2) reducing vaccine cost for parents (e.g., Vaccines for Children program), 3) raising public and provider awareness, 4) monitoring coverage and disease, and 5) improving vaccines and their use. Implementation of this initiative will assist in further increasing coverage to meet the 1996 goals and establishing a vaccination-delivery system that can maintain high coverage levels.

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. 11).

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

  4. CDC. Vaccination coverage of 2-year-old children -- United States, 1992-1993. MMWR 1994; 43:282-3.

  5. ACIP. Haemophilus B conjugate vaccines for prevention of Haemophilus influenzae type B disease among infants and children two months of age and older: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-1).

  6. ACIP. Hepatitis B virus: a comprehensive strategy for eliminating transmission in the United States through universal childhood vaccination -- recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-13).

  7. CDC. Public-sector vaccination efforts in response to the resurgence of measles among preschool-aged children -- United States, 1989-1991. MMWR 1992;41:522-5.

* At least three doses of diphtheria and tetanus toxoids and pertussis vaccine (DTP), polio vaccine, and Haemophilus influenzae type b vaccine (Hib), and one dose of measles-containing vaccine (MCV) (either measles-mumps-rubella, measles-rubella, or measles vaccine). 

** There are two combined series of vaccinations: the 4:3:1 schedule -- four or more doses of DTP/DT, three or more doses of polio vaccine, and one dose of MCV; and the 3:3:1 schedule -- three doses of DTP/DT, three or more doses of polio vaccine, and one dose of MCV.


Monthly Immunization Table

To track progress toward achieving the goals of the Childhood Immunization Initiative (CII), CDC publishes monthly a tabular summary of the number of cases of all diseases preventable by routine childhood vaccination reported during the previous month and year-to-date (provisional data). In addition, the table compares provisional data with final data for the previous year and highlights the number of reported cases among children aged less than or equal to 5 years, who are the primary focus of CII. Data in the table are derived from CDC's National Notifiable Diseases Surveillance System.


Table_1
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TABLE 1. Vaccination coverage levels among 2-year-olds * with vaccines routinely recommended for
children, by vaccination and period -- United States, 1992-third quarter, 1993
==================================================================================================
                                                    First and second
                                  1992               quarters, 1993 +      Third quarter, 1993 +
                          ---------------------    --------------------    ---------------------
Vaccination                 %      (95% CI &)        %      (95% CI)          %      (95% CI)
------------------------------------------------------------------------------------------------
Individual
  DTP/DT @
    >=3 doses             83.0%   (80.8%-85.2%)    87.2%  (84.3%-90.4%)     89.9%  (86.9%-93.0%)
    >=4 doses             59.0%   (56.1%-61.9%)    71.1%  (67.1%-75.1%)     74.8%  (69.9%-79.7%)
  Polio
    >=3 doses             72.4%   (70.1%-74.7%)    78.4%  (74.8%-82.0%)     80.4%  (75.8%-84.9%)
  Hib **
    >=3 doses             28.2%   (25.6%-30.9%)    49.6%  (45.4%-53.8%)     60.3%  (55.0%-65.7%)
  MCV ++                  82.5%   (80.2%-84.8%)    80.8%  (77.2%-84.4%)     85.9%  (82.0%-89.8%)
  Hepatitis B
    >=3 doses              ---         ---         12.7%  ( 9.4%-16.0%)     15.7%  (12.1%-19.2%)

Combined series
  3 DTP/3 polio/1 MCV    68.7%   (66.2%--71.2%)    72.0%  (68.1%-75.9%)     78.7%  (74.2%-83.2%)
  4 DTP/3 polio/1 MCV    55.3%   (52.5%--58.1%)    64.8%  (60.6%-68.9%)     71.6%  (66.7%-76.4%)
------------------------------------------------------------------------------------------------
 * Persons aged 19-35 months.
 + Provisional data.
 & Confidence interval.
 @ Diphtheria and tetanus toxoids and pertussis vaccine or diphtheria and tetanus toxoids.
** Haemophilus influenzae type b.
++ Measles-containing vaccine.
==================================================================================================

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