National, State, and Local Area Vaccination Coverage Among Children Aged 19--35 Months --- United States, 2008

The National Immunization Survey (NIS) estimates vaccination coverage among children aged 19--35 months for 50 states and selected local areas.* Healthy People 2010 established vaccination coverage targets of 90% for individual vaccines in the 4:3:1:3:3:1† vaccine series and 80% for the series.§ This report describes the 2008 NIS coverage estimates for this series and individual vaccines, 7-valent pneumococcal conjugate vaccine (PCV7), ≥2 doses of hepatitis A vaccine (HepA), and hepatitis B vaccination received in the first 3 days of life (HepB birth dose)¶ among children born during January 2005--June 2007. In 2008, 4:3:1:3:3:1 series coverage was 76.1%, compared with 77.4% in 2007; ≥90% coverage was maintained for all recommended series vaccines, except ≥4 doses of diphtheria, tetanus, and acellular pertussis (DTaP) vaccine (1). Coverage with ≥3 doses of Haemophilus influenzae type b vaccine (Hib) decreased from 2007, likely because of the shortage of Hib vaccine and the recommendation to defer the routine Hib vaccine booster dose administered at age 12--15 months (2). Substantial variability was observed in individual and series vaccination coverage among states/local areas. Among racial/ethnic groups,** coverage varied little and, after adjusting for poverty, coverage estimates were not significantly lower for any groups compared with whites. However, children living below poverty had lower coverage than children living at or above poverty for most vaccines. Sustaining high coverage levels and using effective methods of reducing disparities across states/local areas and income groups remains a priority to fully protect children and limit the incidence of vaccine-preventable diseases.

The NIS is an ongoing, random-digit--dialed survey of households with children aged 19--35 months at the time of interview, followed by a mail survey of the children's vaccination providers to collect vaccination information. Data are weighted to adjust for households with multiple telephone lines, household nonresponse, and exclusion of households without landline telephones (3). During 2008, the household response rate was 63.2%; a total of 18,430 children with provider-reported vaccination records were included in this report, representing 71.0% of all children with completed household interviews. Estimates were adjusted using final survey weights to correct for nonresponse (3). Logistic regression was used to control for the effects of poverty to further examine differences among racial/ethnic groups. Statistical differences in vaccination coverage were evaluated using t-tests and were considered statistically significant at p<0.05.

National coverage for the 4:3:1:3:3:1 series was 76.1% in 2008, and coverage estimates for all individual vaccines in the series were ≥90% except coverage with ≥4 doses of DTaP, which was 84.6% (Table 1). PCV7 coverage continued to increase, from 90.0% to 92.8% for ≥3 doses and from 75.3% to 80.1% for ≥4 doses. Coverage with ≥3 doses of Haemophilus influenzae type b vaccine (Hib) decreased from 92.6% to 90.9%. National coverage for ≥2 doses of HepA was 40.4%. HepB birth dose coverage increased to 55.3%, compared with 53.2% in 2007 (Table 1). The percentage of children receiving no vaccinations by age 19--35 months remained at 0.6%.

Estimated vaccination coverage varied substantially among states and local areas (Table 2). State coverage for the 4:3:1:3:3:1 series ranged from 59.2% (Montana) to 82.3% (Massachusetts) and among local areas from 68.5% (northern California counties) to 80.9% (Santa Clara County, California) (Table 2). Among states, HepB birth dose coverage ranged from 19.1% (Vermont) to 81.4% (Arizona) (Table 2).

Little variability in coverage was observed among racial/ethnic groups (Table 3). Among routinely recommended vaccines, only coverage with ≥4 doses of DTaP and ≥4 doses of PCV7 was higher among white children compared with black children. This disparity did not persist after controlling for poverty status.†† Vaccination coverage levels were similar across racial/ethnic groups for the combined 4:3:1:3:3:1 series. After controlling for poverty status, no coverage estimates remained significantly lower for any racial/ethnic group compared with whites. Coverage estimates were lower for children living below poverty compared with those living at or above poverty for the 4:3:1:3:3:1 series and for most vaccines; coverage was lower by 7--9 percentage points for ≥4 doses of DTaP and PCV7 (Table 3). National coverage with ≥3 doses of Hib declined significantly compared with 2007 for children living below poverty (-3.1 percentage points), whereas coverage did not decline significantly for children living at or above poverty (-0.9 percentage points).

Reported by: NA Molinari, PhD, N Darling, MPH, M McCauley, MTSC, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note:

The results from the 2008 NIS, a vaccination coverage survey of children born during January 2005--June 2007, demonstrate that the nation's immunization program (i.e., the U.S. network of federal, state, and local public health officials in partnership with health-care providers and parents) remained successful in maintaining high vaccination rates among young children. However, with approximately 12,000 children born every day in the United States, each requiring protection from vaccine-preventable diseases, continued attention is needed to meet Healthy People 2010 vaccination coverage levels and improve coverage in select groups with lower vaccination coverage.

A significant gap in coverage persists between children who live in poverty and those who do not. This difference suggests that barriers to accessing preventive health care among children living below poverty, such as the underinsured or uninsured, are not fully addressed by programs already in place, such as the Vaccines for Children Program,§§ which covers only the cost of the vaccine. Out-of-pocket costs, such as costs of vaccine administration, well-child visits, transportation, lost time from work, or other locally identified barriers must be addressed to raise coverage among all children who live in poverty (4).

Coverage for ≥3 doses of Hib vaccine declined significantly from 2007 to 2008. Although the cause for this decline cannot be determined solely using data from the 2008 NIS, the decline might be related to changes in vaccination practices, including deferral of the booster dose, resulting from a Hib shortage that began December 2007 and ended June 2009 (2,5). During the shortage, the Advisory Committee on Immunization Practices (ACIP) recommended deferring the booster dose normally administered at age 12--15 months, and although this temporary recommendation did not affect all children surveyed in 2008, it likely affected at least 8%, those who were aged <12 months when the shortage began (CDC, unpublished data, 2009). As Hib vaccine supplies improved, ACIP reinstated the booster dose in June 2009 (2) and recommended that providers administer the booster dose to the deferred children at the child's next routinely scheduled visit or medical encounter (2). In 2009, NIS data collection will include vaccine manufacturer type and a greater proportion of the deferred children, which will allow a more complete examination of the effects of the Hib shortage with subsequent years of data.

The 2008 NIS marks the first time that coverage estimates are routinely reported for the HepB birth dose and for ≥2 doses of HepA among children aged 19--35 months, although previous estimates have been reported¶¶ (6,7). National coverage for HepB birth dose and ≥2 doses of HepA was 55.3% and 40.4%, respectively. Previous data reported HepA coverage for ≥1 doses, not the full 2-dose series, among a subset of children, aged 24--35 months (6). The 2008 NIS is the first survey year to include a majority of children (96%) who were aged <12 months in May 2006, when CDC published the ACIP revision to begin HepA vaccination at age 12--23 months; this allowed measurement of ≥2 doses of HepA coverage among children aged 19--35 months (8). Similarly, most children in the 2008 NIS were born after December 2005 (69%), when ACIP updated the HepB birth dose recommendation to include all medically stable newborns when administering the first dose before hospital discharge (9).

The findings in this report are subject to at least three limitations. First, NIS is a landline telephone survey; although studies indicate that statistical adjustments adequately compensate for noncoverage of households without telephones, nonresponse and noncoverage bias might remain (10). 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 annual national coverage estimates are precise, estimates for state and local areas should be interpreted with caution because of smaller sample sizes and wider confidence intervals.

CDC currently is engaged in many areas of research to address vaccination coverage, including evaluations of interventions at state and local levels to increase vaccination coverage, and surveys to understand physician and parent beliefs about vaccines. CDC continues to encourage use of proven methods of improving coverage, which include parent and provider reminder/recall, reducing out-of-pocket costs, increasing access to vaccination, and multi-component interventions that include education.***

References

1. CDC. Recommendations and guidelines: 2009 child & adolescent immunization schedules for persons aged 0--6 years, 7--18 years, and catch-up schedule. Atlanta, GA: US Department of Health and Human Services, CDC; 2009. Available at http://www.cdc.gov/vaccines/recs/schedules/child-schedule.htm#printable.
2. Updated recommendations for use of Haemophilus influenzae type b (Hib) vaccine: reinstatement of the booster dose at ages 12--15 months. MMWR 2009;58:673--4.
3. CDC. Statistical methodology of the National Immunization Survey, 1994--2002. Vital Health Stat 2005;2(138). Available at http://www.cdc.gov/nchs/data/series/sr_02/sr02_138.pdf.
4. Molinari N, Kolasa M, Messonnier M, Schieber R. Out-of-pocket costs of childhood immunizations: a comparison by type of insurance plan. Pediatrics 2007;120:e1148--56.
5. CDC. Interim recommendations for the use of Haemophilus influenzae type b (Hib) conjugate vaccines related to the recall of certain lots of Hib-containing vaccines. MMWR 2007;56:1318--20.
6. CDC. Prevention of hepatitis A through active or passive immunization: recommendation of the Advisory Committee on Immunization Practices (ACIP). MMWR 2006;55(No. RR-7).
7. CDC. Newborn hepatitis B vaccination coverage among children born January 2003--June 2005---United States. MMWR 2008;57:825--8.
8. CDC. Hepatitis A vaccination coverage among children aged 24--35 months---United States, 2006 and 2007. MMWR 2009;58:689--94.
9. CDC. A comprehensive immunization strategy to eliminate transmission of hepatitis B virus infection in the United States: recommendations of the Advisory Committee on Immunization Practices (ACIP); part 1: immunization of infants, children, and adolescents. MMWR 2005;54(No. RR-16).
10. Molinari N, Wolter KM, Skalland B, et al. Quantifying bias in a health survey: an application of total survey error modeling to the National Immunization Survey. Presented at the annual meeting of the American Association for Public Opinion Research, May 14--17, 2009, Hollywood, FL.

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Date last reviewed: 8/27/2009