National, State, and Local Area Vaccination Coverage Among Children Aged 19--35 Months --- United States, 2006

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The National Immunization Survey (NIS) provides vaccination coverage estimates among children aged 19--35 months for each of the 50 states and selected urban and county areas.* This report describes the findings of the 2006 NIS, which indicated increases in national coverage with pneumococcal conjugate vaccine (PCV) and varicella vaccine (VAR) and a stable coverage level for the 4:3:1:3:3:1 vaccine series (i.e., >4 doses of diphtheria, tetanus toxoid, and any acellular pertussis vaccine [DTaP]^†; >3 doses of poliovirus vaccine; >1 dose of measles, mumps, and rubella vaccine [MMR]; >3 doses of Haemophilus influenzae type b [Hib] vaccine; >3 doses of hepatitis B vaccine [HepB]; and >1 dose of VAR). However, national coverage estimates remained below the Healthy People 2010 target of 90% coverage for PCV, DTaP, and VAR and below the 80% target for the 4:3:1:3:3:1 vaccine series (1). No significant racial/ethnic disparities in 4:3:1:3:3:1 series coverage were observed after controlling for family income. State and local immunization programs should continue to identify and target children who are not fully vaccinated, especially because of low socioeconomic status and other barriers.

To estimate coverage for all age-eligible children, NIS uses a quarterly, random-digit--dialed sample of telephone numbers for each survey area. NIS methodology, including the weighting of respondents to represent the population of children aged 19--35 months, has been described previously (2). During 2006, the household response rate (3) was 64.5%; a total of 21,044 children with provider-reported vaccination records were included in this report, representing 70.4% of all children with completed household interviews. Statistical analyses were conducted using t tests and logistic regression modeling. All tests with p<0.05 were regarded as statistically significant. An income-to-poverty ratio variable^§ was added to logistic regression models to control for racial/ethnic differences in family income, which was calculated using total household income, family size, and household composition and adjusted for annual cost of living using federal poverty guidelines (4).

Estimated national 4:3:1:3:3:1 vaccine series coverage did not change significantly from 2005 (76.1%) to 2006 (77.0%). In 2006, significant increases from 2005 levels were observed for PCV, VAR, and poliovirus vaccine (Table 1). The largest increases were observed for PCV; coverage increased from 82.8% to 87.0% for >3 doses of PCV and from 53.7% to 68.4% for >4 doses.

As in previous years, substantial differences were observed in vaccination coverage among states and local areas (5) for the 4:3:1:3:3:1 vaccine series and individual vaccines. Estimated coverage with the 4:3:1:3:3:1 vaccine series ranged from 83.6% in Massachusetts to 59.5% in Nevada (Table 2). Among local areas, 4:3:1:3:3:1 series coverage ranged from 81.4% in Boston, Massachusetts, to 65.2% in Detroit, Michigan. For vaccines with national coverage estimates below the 90% Healthy People 2010 target (PCV, DTaP, and VAR), PCV (>3 doses) coverage ranged from 96.6% in Rhode Island to 69.9% in South Dakota, DTaP (>4 doses) coverage ranged from 92.6% in Massachusetts to 73.9% in Nevada, and VAR coverage ranged from 96.4% in Rhode Island to 75.7% in Wyoming (Table 2). MMR coverage by state ranged from 97.5% in North Carolina to 84.9% in Nevada (Table 2).

In 2006, vaccination coverage for the 4:3:1:3:3:1 vaccine series was 77.9% for white^¶ children, 77.4% for Hispanic children, 75.9% for Asian children, 74.4% for American Indian/Alaska Native children, and 73.9% for black children (Table 3). Series coverage was significantly lower overall for black children compared with white children. Among black children, coverage ranged from 71.9% (95% confidence interval [CI] = +4.8) among those living below the poverty level to 76.7% (CI = +3.1) among those living at or above the poverty level; among white children, coverage ranged from 69.5% (CI = +4.4) among those living below the poverty level to 78.9% (CI = +1.3) among children living at or above the poverty level. A logistic regression model that controlled for differences in income across racial/ethnic groups revealed no significant difference in coverage between black and white children.

Estimated coverage levels in 2006 for poliovirus vaccine, MMR, Hib vaccine, and HepB were above 90% for all racial/ethnic groups except for American Indian/Alaska Native children for MMR (89.1%) and Asian children for Hib vaccine (89.4%). Levels were below 90% for all racial/ethnic groups for DTaP (>4 doses), VAR, and PCV, except for Asian children for VAR (92.9%) (Table 3). For DTaP (>4 doses), coverage was lower overall among black children compared with white children and lower among all children living below the poverty level compared with all children living at or above the poverty level (p<0.05) (Table 3). For DTaP, the coverage disparity between black and white children was not significant after controlling for family income using the income-to-poverty ratio variable. For PCV (>4 doses), no disparity was observed between black (56.7%; CI = +5.6) and white (60.2%; CI = +4.6) children who lived below the poverty level. A significant disparity in PCV (>4 doses) coverage was observed between black (65.6%; CI = +4.6) and white (72.3%; CI = +1.4) children who lived at or above the poverty level. However, this disparity was not significant after analyses controlled for racial/ethnic differences in family income at or above the poverty level.

Reported by: KG Wooten, MA, N Darling, MPH, JA Singleton MS, A Shefer, MD, Immunization Svcs Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:

Vaccination coverage in 2006 remained at or near record levels for routinely recommended childhood vaccines, but increases in DTaP, PCV, and VAR coverage are needed to reach the 90% Healthy People 2010 target for individual vaccines; these increases would contribute substantially to improved coverage with the 4:3:1:3:3:1 series, particularly among disadvantaged populations. Although coverage with the fourth dose of PCV continued to increase in 2006, a significant disparity was observed among children who lived below the poverty level compared with children who lived at or above the poverty level. Receipt of the fourth dose of PCV might have been deferred for some of the older children in the 2006 NIS cohort (i.e., those born during January 2003--June 2005) because of the vaccine shortage that ended in September 2004 (6).

Results from the 2005 NIS indicated no disparity in 4:3:1:3:3:1 series coverage between black and white children. The results of the 2006 NIS indicate that disparities in coverage by poverty level, coupled with different income distributions among white and black populations, account for the observed coverage disparities between black and white children. A previous report using 1999--2003 NIS data determined that socioeconomic factors had a similar effect on associations between vaccination coverage and race/ethnicity (7). Nearly 41% of all black children aged <5 years live below the poverty level, compared with 16% of white children (8). Children who live below the poverty level are less likely to be vaccinated than children who live at or above the poverty level. The 1999--2003 report led to the development of a questionnaire module of socioeconomic variables that will be added to the NIS in 2008 and will be used to identify barriers to vaccination among racial/ethnic groups and socioeconomically disadvantaged populations. Increasing overall vaccination coverage, eliminating coverage disparities associated with socioeconomic differences in families with children, and eliminating disparities among states and local areas remain high priorities for national, state, and local immunization programs. Vaccination funding through the federal Vaccines for Children program (9) has contributed to record coverage levels among children who are uninsured or underinsured, but additional measures are needed to deliver vaccines to children who live below the poverty level.

The findings in this report are subject to at least three limitations. First, because NIS is a telephone survey, results are weighted to be representative of all children aged 19--35 months. Although statistical adjustments were made to account for nonresponse and households without landline telephones, some bias might remain. Second, underestimates of vaccination coverage might have resulted from the exclusive use of provider-reported vaccination histories because completeness of these records is unknown. Finally, although national estimates of vaccination coverage are precise, estimates for state and local areas should be interpreted with caution because their sample sizes are smaller and their confidence intervals generally are wider than those for national estimates.

Although vaccination-coverage estimates were above the Healthy People 2010 target among all racial/ethnic groups for most of the routinely recommended vaccines, continued collaboration among national, state, local, private, and public partners is needed to reach the 90% target for all vaccines by 2010. Vaccination-coverage data gathered through NIS are used to identify children who are at risk for vaccine-preventable diseases, evaluate the effectiveness of programs designed to increase coverage levels, assess differential impact of vaccine shortages, and track uptake of new vaccines. Expansion of NIS (e.g., adding local areas for coverage assessment; adding survey questions about health insurance coverage, day care participation, and parental beliefs and attitudes regarding vaccines; and including more expansive measures of socioeconomic status) will provide greater understanding of factors associated with low vaccination coverage, particularly those associated with socioeconomically disadvantaged populations.

References

^¶ For this report, persons identified as white, black, Asian, or American Indian/Alaska Native are all non-Hispanic. Persons identified as Hispanic might be of any race.

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